KR100479157B1 - Dual web mail service system using pc mail server and host mail server - Google Patents

Abstract

The present invention is a dual mail service system using a mail server PC and a central mail server, which allows the central mail server to directly send and receive mail to and from the client PC when the mail service is disabled in the mail server PC having a mail server installed on a general PC. The dual mail service system is supported.

The dual mail service system of the present invention comprises: a reception-only SMTP server which receives a received mail from an external SMTP server of a sender and transmits the received mail to a corresponding central mail server; An outgoing-only SMTP server that receives outgoing mail from a central mail server and sends outgoing mail to an external SMTP server of the recipient; Send and receive mails to and from a dedicated SMTP server and a dedicated SMTP server, assign individual user home directories and buffers to multiple mail server PCs, send and receive mails to and from the mail server PCs, and check the mail service of the mail server PCs in real time. If the service is available, the network connection information of the mail server PC is assigned to the mail server address. If the service is unavailable, the network connection information of the user home directory is allocated. The domain name of the mail server is received from the user client PC. At least one central mail server for transmitting network connection information; Establish a mail server on a general PC to send and receive mail through a specific central mail server and network, and send and receive mail to and from the central mail server if a mail service is available, and provide mail services for mail accounts requested by multiple user client PCs. At least one mail server PC; And transmitting the domain name of the mail server PC to the central mail server to receive the network connection information. When the mail server PC is capable of the mail service, the mail server PC accesses the mail server PC with the network connection information to send and receive mail. When the service is unavailable, the network access information includes at least one user client PC connected to the user home directory of the central mail server to receive a mail service.

According to the present invention, a mail server PC having a mail server installed in a general PC provides a mail service to a plurality of mail users, and when the mail server PC is unavailable for other reasons, the central mail server is configured to provide a mail server PC. It has the effect of double supporting mail service by user client PC. In addition, mail server PC users use only when they are working and if they do not work, even if the power off, the central mail server provides the function of the mail server, mail account users are provided with continuous mail service without inconvenience There is.

Description

Dual web mail service system using PC mail server and host mail server}

The present invention is a dual mail service system. More specifically, when a mail server is constructed in a general PC, and a user transmits a mail server and a domain name of a mail server to a central mail server for sending / receiving mail, the central mail is sent. The present invention relates to a system and a method for providing a dual mail service to users by providing network access information of a mail server or a central mail server depending on whether a mail server is capable of mail service.

With the development of the network, e-mails that deliver messages between individuals are increasingly being used instead of the conventional letter mail. Nowadays, e-mail is actively used in areas such as notifications and product advertisements as well as traditional personal correspondence.

In addition, e-mail is a pivotal means of communication in modern society due to its simplicity and ease of writing, and the promptness to arrive at the recipient immediately after sending it.

1 shows a configuration of a conventional mail system 100. The conventional mail system 100 is composed of the sender PC 101, the receiver PC 102, the sender mail server 103, the recipient mail server 104 and the network 105. The sender and the receiver open mail accounts corresponding to their addresses in the mail servers 103 and 104. The mail servers 103 and 104 are divided into an SMTP server and a POP3 server which differ in protocol according to transmission and reception. The process of sending and receiving mail is as follows.

The sender PC 101 runs a mail program, receives an email address of a message and a recipient, and sends an email. The outgoing mail is sent to the SMTP server of the sender mail server 103 and arrives at the recipient mail server 104. The recipient PC 102 receives the mail arriving at its own mail account from the POP3 server of the recipient mail server 104 by running the mail program.

The majority of users open their own mail by signing up to the mail server provided by the large portal site. Users usually receive mail through their mail receiving program through a POP3 server provided by a mail server, or log in directly to a large portal site to check their mail through a web page.

However, in recent years, as a client user has built a homepage on his PC and uses it as a web server, he wants to build a mail server with a web server function on his client PC.

Conventionally, when a mail server PC having a mail server installed in a general PC provides a mail service to a plurality of user client PCs, and when the mail server PC is incapable of other reasons, the mail account requesting the sending and receiving of mail is required. The users had to wait indefinitely until the mail service of the mail server PC was restored normally.

In particular, since a user of a mail server PC uses his PC as a normal PC, there is a problem in that the PC must be operated for 24 hours even when the user does not use the mail server PC.

The present invention is to solve the above-mentioned problems, it is possible to build a mail server PC acting as a mail server on a general PC, and to the domain name of the mail server PC that the client PC transmits for access to the mail server If the central mail server transmits the network connection information of the mail server PC or the central mail server depending on whether the mail server PC is available or not, the central mail server replaces the mail server PC if the mail service of the mail server PC is disabled. An object of the present invention is to provide a dual mail service system using a mail server PC and a central mail server for providing mail services to client PCs.

According to the dual mail service system using the mail server PC and the central mail server of the present invention for achieving the above object, receiving the received mail from the sender's external SMTP server, and transmits the received mail to the corresponding central mail server A receive-only SMTP server; An outgoing-only SMTP server that receives outgoing mail from a central mail server and sends outgoing mail to an external SMTP server of the recipient; Send and receive mail to and from the dedicated SMTP server and the dedicated SMTP server, assign individual user home directories and buffers to a plurality of mail server PCs, send and receive mails to and from the mail server PC, and check whether the mail server PC can receive mail. If the service is available, assign network connection information of the mail server PC to the mail server address, and if the service is unavailable, assign network connection information of the user home directory, and transmit the domain name of the mail server from the user client PC. At least one central mail server for receiving and transmitting the network connection information; Establish a mail server on a general PC to send and receive mail through a specific central mail server and network, and send and receive mail to and from the central mail server if a mail service is available, and provide mail services for mail accounts requested by multiple user client PCs. At least one mail server PC; And transmitting the domain name of the mail server PC to the central mail server to receive the network connection information. When the mail server PC is capable of mail service, the mail server PC is connected to the mail server PC with the network connection information to transmit and receive mail. And at least one user client PC receiving a mail service by accessing a user home directory of the central mail server when the mail service is disabled.

According to a preferred feature of the invention, the central mail server, a receiving mail receiving unit for receiving a receiving mail from the receiving dedicated SMTP server; A received mail management unit for recording the received information of the received mail in a user home directory of a corresponding mail server PC and storing a file of the received mail in a buffer; A received mail information DB for storing the received information including a recipient mail account, a subject, a sender mail account, and a send date of the received mail by the received mail manager; A received mail buffer in which the received mail file is stored by the received mail manager in the order of latest arrival; An outgoing mail receiver configured to receive outgoing mail transmitted by the mail server PC; A sender address search unit for searching whether the recipient mail account of the outgoing mail is a mail account of the same mail server PC, a mail account of another mail server PC, or an external mail account; An outgoing mail delivery unit for delivering outgoing mail to the same central mail server, another central mail server, or the outgoing SMTP server according to the search result of the calling address search unit; And setting up network access information by checking mail service availability for all mail server PCs registered in the central mail server, receiving the mail server address from the user client PC, and the network access information corresponding to the mail server address. Network connection information management unit for transmitting; The network connection information management unit maps the network server connection information of the mail server PC to the mail server address of the mail server PC when the mail service of the mail server PC is available. A network connection information DB for correspondingly storing; Characterized in that comprises a.

In addition, the mail server PC, the receiving mail receiving unit for receiving the latest received mail arrived in real time or at a set time interval from the central mail server; A reception mail transmission unit for receiving a request from the user client PC and receiving the reception mail received by the reception mail reception unit through a network; An outgoing mail receiver for receiving outgoing mails from a plurality of user client PCs; And an outgoing mail delivery unit for transmitting the mail received by the outgoing mail receiving unit to the central mail server. When the mail server PC recovers from a mail service failure, the incoming mail receiving unit does not receive from the central mail server. It is characterized in that for receiving the latest received mail in batches.

Dual mail service system using a mail server PC and a central mail server according to the present invention configured as described above, the general public can provide mail services to users through a mail server PC that has a mail server built on their PC At the same time, it can be used as a personal general purpose client PC. In addition, when the mail account user transmits the domain name of the mail server PC to the central mail server, the mail server user may display the physical network connection information of the mail server PC or the central mail server, depending on whether the mail server PC is capable of mail service. Send to. Therefore, the mail account user is provided with the mail service by transparently accessing the mail server with the network connection information (mail server PC address or central mail server address) received, so that the user can use the dual mail service of the mail server PC or the central mail server. Through this, it is possible to send and receive mail stably.

Hereinafter, a preferred embodiment of the present invention including the above components will be described in more detail with reference to the accompanying drawings.

2 shows a configuration of a dual mail service system 1 according to an embodiment of the present invention. The dual mail service system 1 according to the present invention includes a receiving-only SMTP server 3, a sending-only SMTP server 4, a central mail server 5, a mail server PC 6 and a user client PC 7. It is configured by.

The receiving-only SMTP server 3 manages a plurality of central mail servers 5, each of the central mail servers 5 manages a plurality of mail server PCs 6, and each of the individual mail server PCs 6 A mail service is provided to the user client PC 7.

The receiving-only SMTP server 3 receives the received mail from the sender's external SMTP server 2, searches for which central mail server 5 the recipient mail account belongs to, and receives it to the corresponding central mail server 5. Send the mail.

The central mail server 5 receives the received mail from the SMTP server 3 exclusively for receiving, retrieves the information of the corresponding mail server PC 6 from the mail address, and stores the received mail in the user home directory of the retrieved mail server PC 6. Save incoming mail. In addition, the central mail server 5 serves as a domain name server that manages real-time network access information corresponding to the domain name of the mail server PC 6 by checking whether the mail server PC 6 can perform mail service in real time.

The mail server PC 6 is a mail server built in a general PC. The mail server PC 6 accesses the central mail server 5 in real time or periodically according to user settings, and searches for and receives the latest received mail not yet downloaded.

The user client PC 7 automatically receives a mail service by connecting to the mail server PC 6 or the central mail server 5 depending on whether the mail service is available on the mail server PC 6 (see Fig. 4). If the mail service is available, the user client PC 7 accesses the mail server PC 6 using the network connection information and receives the received mail received in his or her mail account so that the user can check the mail. Display on the screen.

In particular, in the present invention, since the mail server PC 6 is a general general purpose PC rather than an expensive dedicated server equipment, it cannot be guaranteed that the mail server PC 6 is driven for 24 hours. This is because the user of the mail server PC 6 also uses the PC for personal work as a normal client PC user.

Accordingly, in the dual mail service system 1 of the present invention, when the user client PC 7 requests the mail server PC 6 to send / receive mail, the network server of the mail server PC 6 cannot be loaded or not. Even if the mail service is disabled for other reasons such as power off, the user client PC 7 requests the sending / receiving service of the mail to the central mail server 5 so that the mail service can be received at any time.

2, 4, 6a, and 6b, the arrow line indicates O when the mail service of the mail server PC 6 is normal, and X when it is disabled.

3 illustrates a configuration of an integrated central mail server 200 according to an embodiment of the present invention. The reception-only SMTP server 3, the transmission-only SMTP server 4, and the entire central mail server 5 constituting the dual mail service system 1 can be constructed as one integrated central mail server 200.

Distributed and integrated environments each have advantages and disadvantages. The integrated environment is suitable when the number of users of the mail account is easy to manage, and it has the advantage of reducing the load of transmission and reception through other networks. However, the disadvantage is that all the mail service can be stopped when the integrated central mail server 5 is disabled because all management is performed under the control of a single server.

On the other hand, the distributed environment has advantages in terms of resource management that can reduce the burden on the server when the number of users is too large, and has the advantage that the remaining servers can provide a stable mail service in the event of a specific server failure. However, there is a cost of additional equipment burden as high efficiency and stability are obtained.

4 shows an automatic connection function of the user client PC 7 according to an embodiment of the present invention. The automatic connection function in the present invention is implemented through the domain name management of the mail server PC 6 in which the central mail server 5 is designated as the mail server in the client PC 7. That is, the central mail server 5 acts as a domain name server providing the actual address of the physical mail server with respect to the domain name of the mail server PC 6.

When the user client PC 7 wants to connect to the mail server PC 6 for sending and receiving mail, the domain name of the mail server PC 6 is transmitted to the central mail server 5. The central mail server 5 transmits the network connection information of the mail server PC 6 when the mail service is possible or not when the mail service is available on the mail server PC 6. Send network connection information. Here, the network connection information refers to an actual physical address including an IP address and a path name.

Therefore, it is preferable that the central mail server 5 determines whether the mail service of the mail server PC 6 is possible in real time, and according to the real time judgment, the mail server PC 6 or the central mail server is assigned to the domain name of the mail server PC. It is required to match the network connection information of (5). In addition, the mail server PC 6 recovered from the disabled state to the available state receives and updates the details provided by the central mail server 5 directly to the client PC 7 from the central mail server 5 during the disabled state. It is required.

5 shows a detailed structure of components constituting the dual mail service system 1 according to an embodiment of the present invention. Hereinafter, a detailed structure will be described through a mail receiving process and a sending process in the dual mail service system 1 through FIG. 5.

First, the reception process is as follows.

When a sender sends a mail by designating a user having a mail account as a recipient in the dual mail service system 1 of the present invention, the mail is received from the sender's external SMTP server 2 to a receive-only SMTP server 3. .

Receive-only SMTP server 3 according to the present invention comprises a receiving mail receiving unit 31, a receiving address search unit 32, a receiving mail delivery unit 33 and the main DB (321). When the receiving mail receiving unit 31 receives the receiving mail, the receiving address searching unit 32 uses the receiving mail address (for example, aaa@xxx.com), and the receiving mail account of the recipient is stored in the central mail from the main DB 321. Search for belonging to the server 5. According to the information of the central mail server 5 searched by the reception address search unit 32, the received mail is transferred to the corresponding central mail server 5 through the reception mail transmission unit 33.

The central mail server 5 according to the present invention includes a receiving mail receiving unit 51, a receiving mail managing unit 52, a receiving mail information DB 521, a receiving mail buffer 522, an outgoing mail transmitting unit 53, a sending address. And a retrieval unit 54, an outgoing mail receiving unit 55, a network connection information management unit 56, and a network connection information DB 561.

The received mail received through the received mail receiving unit 51 is stored in the user home directory of the mail server PC 6 user corresponding to the recipient mail account by the receiving mail managing unit 52. In the received mail information DB 521 of the user home directory, information such as a recipient mail account, a subject, a sender mail account, and a send date of the received mail are recorded. The mail file 522 built in the user home directory stores the body file of the mail.

In particular, the receiving mail buffer 522 buffers the latest received file within the set storage capacity limit. In addition, the received mail management unit 52 searches for the received mail buffer 522 at the time of the request for transmission of the received mail from the mail server PC 6 or the request of the transfer of the user client PC 7 to select and store the latest received mail. send.

The network connection information management unit 56 checks in real time whether the mail service is possible for all the mail server PCs 6 registered in the central mail server 5 and sets the network connection information in the network connection information DB 561.

Real-time investigation of mail service availability can be configured in two ways. The first is that the network connection information management unit 56 sends a mail request to the mail server PC 6 to check whether the mail service is possible, and the mail server PC 6 responds to the operation state as a mail server. If the central mail server 5 receives a response indicating that it is disabled or does not receive a response, it is determined that the mail service in the mail server PC 6 is disabled. Secondly, when the mail service is available in the mail server PC 6, a signal of periodically available is pushed to the network connection information management unit 56 of the central mail server 5. If the central mail server 5 does not receive a possible signal within a limited time, it is determined that the mail service in the mail server PC 6 is disabled.

The mail server PC 6 according to the present invention comprises a receiving mail receiving unit 61, a receiving mail transmitting unit 62, an outgoing mail transmitting unit 63, and an outgoing mail receiving unit 64. The mail server PC 6 is a general PC with a mail server program installed. It is also desirable to have a web server function. Therefore, users can receive mail account service while using a web server. The receiving mail receiving unit 61 receives the receiving mail from the central mail server 5 and transmits the receiving mail through the receiving mail transmitting unit 62 in response to the request of the user client PC 7. Then, the user receives the client PC 7. Check the e-mail you received.

In fact, when the user runs the mail client program to select the mail retrieval function, the user client PC 7 transmits the domain name of the mail server PC 6 to the central mail server 5. The network connection information management unit 56 of the central mail server 5 retrieves network connection information corresponding to the received domain name from the network connection information DB 561 and transmits it back to the user client PC 7. Here, the user client PC 7 receives the connection path of the mail server PC 6 as network connection information when the mail server PC 6 is in the serviceable state, and the central mail server 5 when the service server is unavailable. Receive the connection path of as network connection information. Therefore, the user client PC 7 automatically connects to the mail server PC 6 or the central mail server 5 according to the network connection information set by the central mail server 5 and receives the received mail.

Next, the calling process is as follows.

When the user composes an outgoing mail using a mail client program installed on the user client PC (7) and selects the outgoing function, the domain name of the mail server PC (6) designated as the mail server is transmitted to the central mail server (5). The network access information is transmitted from the central mail server 5. This network connection information is a URL path including the IP address of the mail server PC 6 or the central mail server 5 depending on whether the mail server PC 6 is capable of mail service as in the above-described reception process.

Assuming that network connection information of the mail server PC 6 has been received, the outgoing mail receiving unit 64 of the mail server PC 6 receives outgoing mail from the user client PC 7. The outgoing mail delivery unit 63 sends outgoing mail to the central mail server 5. In contrast, assuming that the network connection path of the central mail server 5 is received, the outgoing mail receiving unit 55 of the central mail server 5 directly receives outgoing mail from the user client PC 7.

The originating address search unit 54 of the central mail server 5 searches for the recipient mail address of the originating mail and determines where to send it. The outgoing mail delivery unit 53 sends outgoing mail to the same central mail server, another central mail server, or an outgoing dedicated SMTP server 4 according to the determination result. If the same central mail server remains, it is determined whether it is the same mail server PC or another mail server PC.

In the case of an external outgoing mail, the outgoing mail receiving section 42 of the outgoing SMTP server 4 receives the outgoing mail from the central mail server 5. The outgoing mail sender 41 transmits the outgoing mail to the external SMTP server 2 of the outgoing mail receiver.

6A and 6B illustrate a mail transmission / reception environment of the dual mail service system 1 according to an embodiment of the present invention. The dual mail service system 1 of the present invention supports both the webmail service through the server homepage and the POP3 mail service through the mail client program on the client PC.

6A illustrates a webmail service environment. In the case of the webmail service, a mail account user can log in to the homepage of a mail server PC from any PC, and has an advantage of sending and receiving his / her mail through a web interface. The domain name information of the mail server PC 6 that the user directly enters into the address bar of the web browser is the homepage of the mail server PC 6 or the central mail server PC 6 according to the network connection information provided by the central mail server 5. ) 'S homepage. Therefore, if the mail service through the homepage of the mail server PC 6 is unavailable for other reasons, the user client PC 5 logs in to the homepage of the central mail server 5 and transmits and receives its own mail.

6B shows a mail service in a POP3 server environment. A user sets his or her mail account access information (e-mail address, password), POP3 server information, and SMTP server information in his mail client program, and sends and receives mail through the mail program. As the POP3 server information and the SMTP server information, information composed of the domain name of the mail server PC 6 is set. POP3 server environment has the advantage that the user can easily send and receive mail through the mail program without having to log in by entering the ID and password every time on the mail server PC (6).

As described above, an embodiment of the dual mail service system using the mail server PC and the central mail server according to the present invention is constructed. Although the present invention has been described by way of limited embodiments and drawings, the present invention is not limited thereto, and the technical spirit of the present invention and the claims to be described below by those skilled in the art to which the present invention pertains. Of course, various modifications and variations are possible within the scope of equivalents.

In the dual mail service system using the mail server PC and the central mail server according to the present invention, a mail server PC having a mail server installed on a general PC provides a mail service to a plurality of mail users. If not, the central mail server assigns the central mail server's connection information to the domain name of the mail server PC and provides the central mail server's connection information to the user's client PC so that the user's client PC can Dual mail service is provided.

In addition, since the mail server PC can operate as a normal PC at the same time as the mail server function, the central mail server provides the function of the mail server even when the user uses it only when he or she does not work. Therefore, even in the process where the function as a mail server and the function as a normal client PC are in parallel with each other, the mail account users are continuously provided with the mail service without any inconvenience.

The following drawings attached to this specification are illustrative of preferred embodiments of the present invention, and together with the detailed description of the invention to serve to further understand the technical spirit of the present invention, the present invention is a matter described in such drawings It should not be construed as limited to

1 is a block diagram of a conventional mail system.

2 is a block diagram of a dual mail service system according to an embodiment of the present invention.

Figure 3 is a block diagram of a central mail server built as an integrated server according to an embodiment of the present invention.

4 is a conceptual diagram of an automatic connection function of a user client PC according to an embodiment of the present invention.

5 is a detailed structural diagram of components constituting the dual mail service system according to an embodiment of the present invention.

6A and 6B are diagrams illustrating a mail environment of a dual mail service system according to an embodiment of the present invention.

7 is a flow chart of a dual mail service method according to an embodiment of the present invention.

8 is a flow chart of a mail server PC registration process in the central mail server according to an embodiment of the present invention.

9 is a flow chart of a user mail account registration process in a mail server PC according to an embodiment of the present invention.

10 is a detailed procedure of the mail server PC availability check step of the central mail server according to an embodiment of the present invention.

11 is a flowchart illustrating a process of receiving a received mail from a receiving-only SMTP server to a mail server PC according to an embodiment of the present invention.

12 is a flow chart of a received mail receiving process of a user client PC according to an embodiment of the present invention.

Figure 13 is a flow chart of the outgoing mail sending process of the user client PC according to an embodiment of the present invention.

14 is a flow chart of the outgoing mail transmission process of the central mail server according to an embodiment of the present invention.

Explanation of symbols on the main parts of the drawings

1: Dual mail service system 2: External SMTP server

3: Dedicated SMTP server 4: Dedicated SMTP server

5: Central mail server 6: Mail server PC

7: User Client PC 51: Receiving Mail Receiving Unit

52: incoming mail management unit 53: outgoing mail delivery unit

54: outgoing address search unit 55: outgoing mail receiving unit

56: network access information management unit 61: receiving mail receiving unit

62: receiving mail transmission unit 63: outgoing mail transmission unit

64: outgoing mail receiver

Claims (6)

A reception-only SMTP server which receives the received mail from the sender's external SMTP server and sends the received mail to a corresponding central mail server; An outgoing-only SMTP server that receives outgoing mail from a central mail server and sends outgoing mail to an external SMTP server of the recipient; Send and receive mail to and from the dedicated SMTP server and the dedicated SMTP server, assign individual user home directories and buffers to a plurality of mail server PCs, send and receive mails to and from the mail server PC, and check whether the mail server PC can receive mail. If the service is available, assign network connection information of the mail server PC to the mail server address, and if the service is unavailable, assign network connection information of the user home directory, and transmit the domain name of the mail server from the user client PC. At least one central mail server for receiving and transmitting the network connection information; Establish a mail server on a general PC to send and receive mail through a specific central mail server and network, and send and receive mail to and from the central mail server if a mail service is available, and provide mail services for mail accounts requested by multiple user client PCs. At least one mail server PC; And The domain name of the mail server PC is transmitted to the central mail server to receive the network connection information. When the mail server PC is available for mail service, the mail server PC is connected to the mail server PC with the network connection information to transmit and receive mail. At least one user client PC that receives a mail service by accessing a user home directory of the central mail server using the network access information when the mail service is unavailable. Dual mail service system using a mail server PC and a central mail server, characterized in that comprises a. The method of claim 1, The reception-only SMTP server, A reception mail receiving unit which receives a reception mail from the external SMTP server through a network; A reception address search unit for searching a main DB with a recipient mail address of the received mail and searching a user home directory of a corresponding central mail server; And A reception mail delivery unit for delivering the reception mail to the central mail server that holds the user home directory searched by the reception address search unit; Dual mail service system using a mail server PC and a central mail server, characterized in that comprises a. The method of claim 1, The outgoing dedicated SMTP server, An outgoing mail receiving unit for receiving an outgoing mail from the central mail server; And An outgoing mail sender for sending the outgoing mail received by the outgoing mail receiver to an external SMTP server of a corresponding receiver through a network; Dual mail service system using a mail server PC and a central mail server, characterized in that comprises a. The method of claim 1, The central mail server, A reception mail receiving unit which receives a reception mail from the reception-only SMTP server; A received mail management unit for recording the received information of the received mail in a user home directory of a corresponding mail server PC and storing a file of the received mail in a buffer; A received mail information DB for storing the received information including a recipient mail account, a subject, a sender mail account, and a send date of the received mail by the received mail manager; A received mail buffer in which the received mail file is stored by the received mail manager in the order of latest arrival; An outgoing mail receiver configured to receive outgoing mail transmitted by the mail server PC; A sender address search unit for searching whether the recipient mail account of the outgoing mail is a mail account of the same mail server PC, a mail account of another mail server PC, or an external mail account; An outgoing mail delivery unit for delivering outgoing mail to the same central mail server, another central mail server, or the outgoing SMTP server according to the search result of the calling address search unit; And It checks whether the mail service is possible for all the mail server PCs registered in the central mail server, sets network access information, receives the mail server address from the user client PC, and sends the network access information corresponding to the mail server address. Network connection information management unit for transmitting; The network connection information management unit maps the network server connection information of the mail server PC to the mail server address of the mail server PC when the mail service of the mail server PC is available. A network connection information DB for correspondingly storing; Dual mail service system using a mail server PC and a central mail server, characterized in that comprises a. The method of claim 1, The mail server PC, A receiving mail receiving unit which receives the latest received mail received from the central mail server in real time or at set time intervals; A reception mail transmission unit for receiving a request from the user client PC and receiving the reception mail received by the reception mail reception unit through a network; An outgoing mail receiver for receiving outgoing mails from a plurality of user client PCs; And An outgoing mail delivery unit for transmitting the received mail to the central mail server; Consisting of, When the mail server PC recovers from the mail service failure, the mail server PC and the dual mail server using the central mail server, characterized in that the receiving mail receiving unit receives the latest received mail not received from the central mail server collectively Mail service system. The method of claim 1, The central mail server or the mail server PC, A web server having a homepage is constructed to provide a webmail transmission / reception service of a specific mail account requested by the user client PC through the homepage, Or a POP3 server is provided to provide a mail transmission / reception service of a specific mail account through a mail program installed in the client PC.