Postfix SMTP Error (10.3.9)

[srciaran]

I have been running Mail services under Mac OS X Server 10.3.9 for a few days now, and I am seeing an error at least once a day, sometimes twice. Mail.app produces a SMTP error and cannot send mail any more. I have to restart the Mail service (sometimes twice) before it starts working again. I have checked the SMTP log, and the entry that seems to apply looks like this:

Jul 22 12:49:20 AGWebServer postfix/postfix-script: stopping the Postfix mail system
Jul 22 12:49:20 AGWebServer postfix/master[21088]: terminating on signal 15
Jul 22 12:49:20 AGWebServer postfix/master[11023]: daemon started -- version 2.0.10
Jul 22 12:49:27 AGWebServer postfix/postfix-script: stopping the Postfix mail system
Jul 22 12:49:27 AGWebServer postfix/master[11023]: terminating on signal 15
Jul 22 15:42:22 AGWebServer postfix/postfix-script: fatal: the Postfix mail system is not running
Jul 22 15:42:22 AGWebServer postfix/master[13413]: daemon started -- version 2.0.10
Jul 22 15:42:29 AGWebServer postfix/postfix-script: stopping the Postfix mail system
Jul 22 15:42:29 AGWebServer postfix/master[13413]: terminating on signal 15
Jul 22 15:43:03 AGWebServer postfix/postfix-script: fatal: the Postfix mail system is not running
Jul 22 15:43:03 AGWebServer postfix/master[13433]: daemon started -- version 2.0.10
Jul 22 15:43:13 AGWebServer postfix/postfix-script: stopping the Postfix mail system
Jul 22 15:43:13 AGWebServer postfix/master[13433]: terminating on signal 15
Jul 22 15:43:14 AGWebServer postfix/master[13443]: daemon started -- version 2.0.10

What's happening here?