Zimbra has been running well for a week now. Yesterday morning I get a call saying that one of our users can't access their email (in outlook.) i try to access the 7071 zimbra admin, but that page doesn't come up. additionally the webmail doesn't work either. I ssh in and "service zimbra restart"

the only thing I noticed was that on the service shutdown, the smtp part failed to shutdown (probably because it had already abnormally shutdown.)

Everything came up fine and is working well again.

How do I track down the root cause of this problem? Which logs would provide me with clues as to what went wrong?