[Dovecot] High load with Thunderbird

Hello, all.

I'm using Dovecot 1.0.15 on our internal mail server and I'm seeing a high load from one of our users.

This user uses Thunderbird (with the IMAP protocol) and the load average of the server goes through the roof every once in a while. I'ld like to understand why we're seeing this and whether the blame should be put on Thunderbird or on Dovecot.

Has anyone ever seen this before?

Emmanuel