Yesterday I experienced an issue with our mailbox (tomcat) being stopped. I'd restart it and a few minutes later it would stop again. I had to do this about 8-10 times over the next hour while simultaneously looking through the logs. It stopped crashing just after 5 pm or so. I was able to find that there were repeated entries in the mailbox.log saying "java.lang.OutOfMemoryError: Java heap space". It was always for the same user and always during a message send. Turns out the user turned off their PC at 5pm and went home - right when the crashing stopped.

Today I was able to confirm that they have an email stuck in their outbox and every attempt to deliver results in this heap error and usually every 3rd or 4th attempt results in tomcat crashing completely.

As for the message, it doesn't appear to be too unusual. It is a reply to a mass email of about 30 people. He's attempting to reply to all 30 of them and then CC 2 other. I sent myself a test message from his account which does leave the inbox, but the stuck message stays stuck.

Obviously, deleting this email will stop this instance of the problem - but I want to prevent it from happening again with him or anyone else.

Specifics:
server is a VMWARE VM running with 2G of RAM and 2 cores assigned. There are about 75 total mailboxes on this server. Zimbra version is Network Edition 4.5.5. User is on XP Pro with Outlook 2003 and Zimbra ZCS 4.5.230.0.

What I find most disturbing is that outlook can bring down the Web Client and Web admin client.

I appreciate any help or troubleshooting/prevention advice.