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I have a Plesk server running Postfix on Ubuntu 10.04 and the SMTP service on port 25 is down. When I stop and then start postfix the server comes up only for a minute and goes down again. I have checked the load on the server and it is low as shown:

top - 04:29:33 up 19 days,  3:25,  4 users,  load average: 1.47, 1.78, 2.34
Tasks: 936 total,   1 running, 935 sleeping,   0 stopped,   0 zombie
Cpu(s):  0.7%us,  0.3%sy,  0.0%ni, 86.6%id, 11.7%wa,  0.6%hi,  0.1%si,  0.0%st
Mem:   6110496k total,  6072988k used,    37508k free,   251244k buffers
Swap: 12000544k total,    95264k used, 11905280k free,  4370432k cached

IMAP clients are not experiencing a problem and there are no issues with receiving emails for both POP or IMAP. Only SMTP (port 25) is a problem. If I ask clients to use the submission port (587) messages are delivered.

netstat -lnt shows the following results, so it's not a port issue.

tcp        0      0    *               LISTEN     
tcp        0      0  *               LISTEN  
share|improve this question
Check your logs for error messages. /var/log/mail.log is a good place to start. I like to grep -iv connect mail.log as long as I know it's not a connection issue. Also grep postfix *log can find messages that have gone to other log files. – Ladadadada Jul 3 '12 at 6:09
up vote 3 down vote accepted

If netstat is showing something listening on 25 but your mail transfer agent is not it, then yes, you have a "port issue." Postfix can't bind to its preferred port.

Use netstat -tulpn to find the process ID and kill it, then try starting Postfix.

share|improve this answer
The -p option requires root. Don't forget to prepend sudo if you are running as a normal user. – Ladadadada Jul 3 '12 at 6:03

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