Woke up this morning and the Postfix SMTP server on Ubuntu 10.04 and Plesk stopped running.

I could start and stop via service
# service postfix start

and it appeared everything was working fine. However, it wasn’t until I looked at the syslog /var/log/syslog that I saw an error occurring on start up.

Nov 26 12:51:27 blue postfix/tlsmgr[28017]: fatal: open database /var/lib/postfix/smtpd_scache.db: Invalid argument
Nov 26 12:51:29 blue postfix/master[28012]: warning: process /usr/lib/postfix/tlsmgr pid 28017 exit status 1
Nov 26 12:51:29 blue postfix/master[28012]: warning: /usr/lib/postfix/tlsmgr: bad command startup — throttling

SOLUTION:
1. stopped postfix: # service postfix stop
2. deleted the cache files friom /var/lib/postfix
# rm /var/lib/postfix/smtpd_scache.db
and
# rm /var/lib/postfix/smtp_scache.db
3. restarted postfix and voila, everything works: # service postfix start

hope this helps!