this is on a ZCS5.0.13(OSS) system, we found there's some error message in mailbox.log file :
the /opt/zimbra is located in the SAN storage and OS root file system and /opt/zimbra don't have disk space problem at that time.
2010-03-08 09:07:06,782 ERROR [LmtpServer-562870] [email@example.com;mid=35278;] Sieve - Evaluation failed. Reason: null
2010-03-08 09:07:06,782 INFO [LmtpServer-562870] [firstname.lastname@example.org;mid=35278;] lmtp - try again for message email@example.com: exception occurred
does anyone see this before and any idea what's it for?