[imp] filtering slowness problem

[Tom Kwong]

For some reasons, imp gets slower and slower.   Recently, it has been 
taking 50+ seconds just to login from Horde. 

I found that the problem came from filtering, i.e. if I disable both 
filtering options 1) apply filters upon login and 2) apply filters when 
inbox is displayed, then it's very fast.  I only have 10 or so filters 
that matches only the subject line and they all stop checking if the 
rule matches, and they only apply on unseen messages.  There are only 30 
or so unseen messages in my Inbox so I can't understand why filtering 
takes so long.

The top command shows imapd taking 90%+ cpu during the login process. 
Any idea?  Thanks advance for your help.

Tom