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 0.0.0.0:25 0.0.0.0:* LISTEN tcp 0 0 0.0.0.0:8443 0.0.0.0:* LISTEN