smtp server chokes

I am running netscape Messaging server 4.15patch 2 on solaris 2.6. Once in a week the smtp server chokes,as result all my outgoing mails are stuck in outbox of outlook express.Pop3 is fine...only the smtp chokes.
[226 byte] By [708740] at [2007-11-25 7:09:28]
# 1

Install Solaris Patches, use pfiles and pmap to see what is going on with the SMTP Deamon. I believe you will find that there are several problems with patch 2 of Messaging. Upgrade to patch 6.

DO NOT UPGRADE TO PATCH 7, it has a nasty memory leak in the mailbox-deliver subroutine of the SMTP Deamon.

Jaime Cardoso at 2007-6-29 17:41:01 > top of Java-index,E-Mail, Calendar, & Collaboration,Sun Java System Messaging Server...