I can reproduce this problem on two separate installations of Zimbra 3.2 running on Dell Xeon 3ghz/2gb RAM - 20 mailboxes and AMD64 3200/4gb RAM - 4 mailboxes. Both using CentOS Linux.
Here's the problem: when a user sends an email with 3mb attachment, it causes prolonged delays in Zimbra and most noticeably the Zimbra Web Calendar UI for ALL USERS.
This problem occurs both during high usage (all users sending/receiving) as well as low usage (when I was the only user sending email, other users still receiving).
Typical response times for changes to the Calendar goes from <2 seconds to >8 seconds up to 12 seconds. This is for such operations as simply moving Calendar entry date/times and saving new Calendar entries.
This delay will last for between 2 to 5 minutes after the email was sent. And after this time the usual responsiveness is restored (<2 seconds).
Has anyone seen this before? And any ideas on how this can be resolved?