Linux mail server

One, the e-mail system consists of five parts:

1. MUA ( Mail User Agent ) Mail User agent

mua

Common tools: foxmail , outlook , webmail , mail Command and so on. Send mail using protocol: smtp

2. MTA ( Mail Transfer Agent ) Mail Delivery Agent

MTA responsible for the storage and forwarding of messages ( Store and forward ). the MTA monitors the user agent's requests, finds the corresponding mail server based on the destination address of the e-mail message, transmits the letters between the servers and buffers the received messages.

Common tools: windows under: exchange , linux sendmail , postfix , qmail ET.

3. M SA mail Submition agent ) message submission Agent

msa responsible for messages by mta All preparatory work and error detection that must be done before sending, msa mua and mta mua The information is first-class information to be detected. When a server colleague receives too many send requests, it queues them and submits them to mta

4. MDA ( Mail Delivery Agent ) Mail Delivery Agent

MDA from MTA receive messages and make appropriate local deliveries that can be posted to a local user, a mailing list, a file, or a program. Common tools:procmail,maildrop and so on. Can implement spam filtering, virus mail filtering, and so on.

5. M Ra/maa Mail retrieval/access agent ) message Access Agent

MAA used to connect users to the System mail library, using the POP or IMAP agreement to collect mail.

Common tools: Uw-imap , Cyrus-imap , Courier-imap and so on.

Second, the Mail sending and receiving process:

start, use Mail user agent(MUA)An e-mail message was created that was sent to the user's mail transport agent after it was created(MTA)--the transfer process uses aSMTPagreement. ThenMTAcheck the recipient of the message toDNSThe server queries the receiving partyMTAthe corresponding domain name, and then send the message to the receiving partymta--the use is stillSMTPagreement. At this point, the message has been sent from the remote user station to hisISPMail server and forwards it to your domain.

    However, The message is likely to be transferred to another mta mta take over this email and deliver it. At this point, mta The message is delivered to a message delivery agent (MDA) mda The main role is to save the message to a local disk, some mda mda

Finally, check the email. Running MUA, you can use the IMAP protocol or the POP3 protocol to query your mail server for your messages. The mail server confirms your identity, then retrieves the mailing list from the message store and returns the list to MUA. Now you're ready to read the mail.

Third, the description:

1 mua ( Mail User Agent)

from mta get mail and through mta The tool that sends mail, which generally supports smtp and pop agreement. such as: outlook foxmail

2 , MTA (Mail Transport Agent)

fitted MTA server can be called a mail server. There are three main functions of the MTA:

throughPopAgreement andMUACommunication, putMTAMessages in the mail box are delivered toMUA (alsoMUAin theMTAThe process of fetching mail);[personal feeling here to putMAAMergingMTAthe]

through the SMTP protocol, receives the user through The MUA drafts the new mail, and prepares to send the mail;

through the SMTP protocol, select the appropriate route between the different MTA on the network and eventually deliver the message to the target mail server ( That is, the message is on the source server to the destination server. Delivery Process ) .

3 , MDA (Mail Delivery Agent)

can be seen as MTA a sub-module to achieve mail delivery, analysis, filtering, automatic reply and other functions

4 , WEB Mail

    Now many people do not use the mua Most of the mail writing and sending and receiving is through the Web page, so on the server added a web server, in the web is typically used in a server cgi program, by verifying the identity of the user and then providing the web page Let it send and receive mail. The process is simply to save the process of downloading and sending from the server.

    Because the early network is unreliable, in order to make the mail can be sent to the other side of the host, all open the open relay, that is, not to the local will help forward. But this may be exploited, so later added the  sasl simple Authentication Security Layer Simple authentication security layer. Function: When the client sends mail to the server, first check whether the original account and password is on this server, if yes, forward it. sasl is a software , there is saslauthd

5 linux mail server:

1. Create DNS of the MX Record
2. Create SMTP
3. Deployment SASL Certified Users
4. Deployment WEB server, database server
5. Install pagers, spam filters, etc.

Linux mail server