Configuration installation for SendMail under Linux

With the development of Internet, e-mail has grown rapidly into a major network information transfer tool. Faced with the demand for fast, inexpensive, and highly reliable e-mail, many companies and individuals use the services provided by Linux as a solution to meet these needs.

SendMail was originally written by Eric Allman in 1979. It first ran on the BSD 4.0 platform. But the program is not flexible enough to be reconfigured every time you compile it. With the TCP protocol and other developments, its own inflexibility has clearly failed to meet the growing demand. Eric Allman decided to rewrite the SendMail, which gave birth to the current MTA standard. This is a brief introduction to SendMail. Our article is mainly to demonstrate how to use the configuration SendMail8.11.2 service on a newly installed Redhat 7.1 to frame your e-mail server.
redhat7.1 The default installation time for the SendMail 8.11 service is installed. Because Redhat installation is very simple, we ignore the installation process here, please refer to the relevant information Redhat The document on the CD. To make your new e-mail server work correctly, you must first troubleshoot DNS issues. Add the hostname and IP address of your e-mail server to DNS and confirm with Nslookup:

[root@testmail/root]# Nslookup-sil testmail.blank.com
server:192.168.100.1
address:192.168.100.1#53

Name:testmail.blank.com
address:192.168.100.134

You also have to try the reverse Domain name resolution, which is important to prevent message latency. Most mail servers now use the reverse domain name resolution as part of the authentication of the mail message. So using your IP address to try the reverse Domain name resolution is correct.

[root@testmail/root]# Nslookup-sil 192.168.100.134
server:192.168.100.1
address:192.168.100.1#53

134.100.168.192.in-addr.arpa name = TESTMAIL.blank.com.

As you can see, the DNS service is working properly, so let's go ahead and configure the SendMail service. Redhat 7.1 The default installation already enables the SMTP service to run on the local computer.

You use NETSTAT-NL to see all the daemons listening to the port, note this line: 127.0.0.1:25, this means that the SendMail service is already listening on the local (SMTP) port:

[root@testmail/root]# NETSTAT-NL
Active Internet connections (only servers)
Proto recv-q send-q Local address Foreign
TCP 0 0 0.0.0.0:32768 0.0.0.0:* LISTEN
TCP 0 0 0.0.0.0:111 0.0.0.0:* LISTEN
TCP 0 0 0.0.0.0:22 0.0.0.0:* LISTEN
TCP 0 0 127.0.0.1:25 0.0.0.0:* LISTEN
UDP 0 0 0.0.0.0:32768 0.0.0.0:*
UDP 0 0 0.0.0.0:667 0.0.0.0:*
UDP 0 0 0.0.0.0:111 0.0.0.0:*
Active UNIX domain sockets (only servers)
Proto refcnt Flags Type State I-node Path
UNIX 2 [ACC] STREAM listening 1119/dev/gpmctl
UNIX 2 [ACC] STREAM listening 1172/tmp/.font-unix/fs7100