Help

Firstly, lets try understand that receiving mail and sending mail are handled by two different programs.
Generally when you are sending mail you are talking to a program like Sendmail or Exim. When you are receiving mail, you are talking to a POP3 or IMAP program like qpopper or dovecot. If you understand this concept, you will find it easier to troubleshoot mail problems.

If your users cannot send email, then the place to start looking is with Sendmail or Exim. We will concentrate on Sendmail here, as most of our servers are using it.

Firstly, we need to check if the sendmail program is actuall running.

ps ax | grep sendmail

shows us that it is.

[root@server ~]# ps ax | grep sendmail
3377 ? Ss 0:02 sendmail: accepting connections
3385 ? Ss 0:00 sendmail: Queue runner@01:00:00 for /var/spool/clientmqueue

If sendmail is not running, its easy to start it with..

service sendmail start

Secondly, we need to check if we can talk to sendmail.

telnet localhost 25

shows us that we can.

[root@server ~]# telnet localhost 25
Trying 127.0.0.1...
Connected to localhost.localdomain (127.0.0.1).
Escape character is '^]'.
220 server.company.co.zw ESMTP Sendmail 8.13.1/8.13.1; Wed, 20 Dec 2006 08:02:17 +0200

Generally, if you have problems sending a message, the error that Sendmail will generate and show you on the screen will point you in the right direction. The most common error is when people send to multiple recepients, and one of the addresses is incorrect, it will generate a message saying "user unknown"