SMTP Basic e-mail Sending protocol principle

1. E-Mail SendingThe client is sent to the server side, and the Postfix software provides MTA,MDA. MTA provides SMTP service, accepts mail (reads DNS MX record)--"Save MDA transfer mail MUA user agent
1-1 the server submits the e-mail message to TCP port 25 by using the SMTP protocol, or by a local client
/usr/bin/sendmail the program for submission. If the MTA is the final target location, the message is passed to the MDA.
Otherwise, the MX record is used to find the next MTA in DNS and to use SMTP for forwarding. 1-2.MDA: "Mail send Agent". The MDA sends the message to the recipient's local message store (by default,
/var/spool/mail/user). Postfix provides its own MDA to send to a file-based local default message
Storage location/usr/libexec/postfix/local.1-3. Forwarding: The e-mail server (MTA) forwards the submitted messages to another server for sending 1-4. Queued: Failed send or forward attempts queued and retried by the MTA definition. (By default, Postfix per hour
Do this one time) 1-5. Reject: E-mail was rejected by the e-mail server during the first commit 1-6. Return: After the remote server accepts e-mail for delivery, it returns the e-mail message to the originating e-mail Service
Email to the originating e-mail server and/or user e-mail for sending
or user
The 2-1postfix is provided by the postfix RPM package and controlled by the Postfix service script. It is a collaborative operation by multiple
The program consists of a modular program, whose components are controlled by the master process. 2-2postfix's master profile is/ETC/POSTFIX/MAIN.CF, you can use a text editor or postconf command to enter the
Line edit. The postconf command can also be used to determine all current and default configuration settings for Postfix or to determine the
Some settings. 2-3 by default, Postfix listens only for incoming e-mail from localhost. To reconfigure Postfix to receive
For local mail sent from a remote host, you must set inet_interfaces = All2-4 to troubleshoot the e-mail in/etc/postfix/main.cf, and all mail-related operations logs will be kept in/var/log/maillog.
This includes information about the events and success events. The MAILQ command (or postqueue-p) displays the queued
There is a list of outgoing messages. To try to send all queued messages again immediately, you can run the Postfix flush
(or postqueue-f); otherwise, Postfix will attempt to resend about once per hour until the message is accepted or
Period.
3. Important Postfix Configuration Instructions
All of the following instructions can be found in the/etc/postfix/main.cf file. 3-1 Myorigin
Rewrite the locally published e-mail message so that it appears as from the domain. This helps ensure that the response is returned to the inbound mail server
Default: Myorigin = $myhostname 3-2 inet_interfaces
Controls the network interface on which Postfix listens for incoming e-mail. If set to Loopback-only, listen only
127.0.0.1 and:: 1,
If all is set, all network interfaces are listening. You can also specify a specific address.
Default: inet_interfaces = localhost3-3 mydestination
e-mail messages that receive addresses for these domains are passed to the MDA for local delivery.
Default: mydestination = $myhostname, localhost. $mydomain, localhost3-4 Mynetworks
A comma-separated list of IP addresses and networks (in CIDR notation). These addresses and networks can be transferred through this MTA
to any location without further authentication.
Default: Mynetworks = 127.0.0.0/83-5 relayhost
Relayhost forwards all outbound messages that are passed. Typically specified in square brackets to prevent MX record lookups.
Default: Relayhost =3-6 local_transport
How to send a message with a $mydestination address. By default, set to
Local: $myhostname (using the local MDA to send incoming e-mail to the/var/spool/mail
Local mail store location)
Default: Local_transport = Local: $myhostname 3-7 postconf-d displays default values.
POSTCONF-N displays changes that differ from the default values.

4. Shell mail client (to create a new shell for the server to protect data security. )
In fact, most organizations no longer use only one mail server to process all inbound and outbound e-mails. Instead, out of
Security Considerations The mail server is set up specifically for a specific role so that it can be targeted to the specific
Better standard roles with programs include:
1) NULL client: A client computer running the local MTA so that all e-mail messages can be forwarded to the Central Mail Service
The client does not accept local sending of any e-mail messages.
2) Inbound mail server only: Process all incoming e-mail from the user at the site and pass it to the MDA to send to
The mail server where the user's mail is stored. In practice, the reverse is typically installed on the front-end of the inbound mail server only
A spam server or a standby to filter spam and forward only normal mail to an inbound mail server.
3) Outbound Mail forwarding: Outbound mail forwarding (or "smarthost") receives all outbound mail, and uses MX records and
The SMTP protocol forwards the message to the target location.

This article from the "Technology life, Simple not simple" blog, please be sure to keep this source http://willis.blog.51cto.com/11907152/1850900

SMTP Basic e-mail Sending protocol principle