Best fs for imapserver?

[Eric Persson <eric@persson.tm>]

I'm looking to improve the performance on one of our imap-servers since 
its getting slow on large folders with 100k or more files in them. The 
imapserver is courier imap(using maildir format), and I'll hope to keep 
that as of now.

However, I read that reiserfs was more efficient than ext3 handling lots 
of small files, which sounds like a good choice for this application. 
But is there other options? Is reiserfs the best choice?

Hints, personal experience, feedback would be interesting.. :)

/eric