Hello everybody!
Some time ago I tried Roundcube (0.1-beta) but faced this same exact problem... I was in a hurry so I just went over to Ilohamail, now a few months have passed and decided to give Roundcube another try (now with the SVN version) since I find it very nice.
Apache 2.0.55
FreeBSD 6.0
MySQL 5.0.18
dbmail 2.0.7
Everything works ok by itself, so in general I doubt there's any problem with the configuration of those.
The problem is the following. Roundcube seems to work ok (actually it does) but most of the times when an user logs in and retrive the listing of his messages leaves the corresponding http process in an infinite loop that takes 100% CPU time. Roundcube keeps working ok but at every request every new httpd child that answer the request start looping as well until, when 6/7 copies of httpd allocate all the processor time, apache stops responding or respond very slowly.
After a couple of minutes (when the PHP's script timeout kicks in, I suppose) the httpd children start to close and everything gets back to normal again.
To me it looks like an infinite loop somewhere in roundcube code. I tried to track down where the problem may be but could not find any clue.
Here are my hints:
1) the problems kicks in when logging in, but after all the processing has been done, since the output to the client looks perfect: there even is the