[imp] IMP shared folders and iMS: a warning

[Sheeri Kritzer]

So, yesterday we got bitten.

When IMP queries the imap server for a list of a user's folders, it uses the "list %" command.  According to Chuck H, list % should *only* look through the top level of a user's folder.

However, in iMS (we're running version 5.2 on Solaris 8), list % looks through ALL the folders on the server.  And it does it poorly.  The result was that we had huge loads (up to 600!) on our IMAP servers, and users were having unnacceptable delays while using webmail (3-5 minutes to do anything, because CPU load was so high).

We found that the breaking point was about 100 clients simultaneously trying the list % command.  

This is a SUN bug to which they've offered two possible fixes. There is
a "hotfix" kit, which contains patches that are not fully tested. The
second fix turns off shared folders. As we do not currently offer
shared folders as a feature in IMP, we just went ahead and disabled shared folders in iMS.

I hope this helps someone; yesterday was pretty bad here for us, with all the students back for the semester and faculty and staff back from a long weekend (our faculty IMAP server broke, in hindsight predictably, at 9:12 am).

-Sheeri Kritzer
Systems Administrator
University Systems Group
Tufts University
617-627-3925
sheeri.kritzer@tufts.edu