This is an old revision of the document!
http://www.getthunderbird.com/
Thunderbird is a free, extensible mail client software with excellent IMAP support.
http://enhancedlinux.com/2010/01/15/disable-thunderbird-3-bloat/
Thunderbird caches local copies of your message store in your Windows profile. If you have Roaming Profiles, this can negatively affect your login/logout times.
Edit (Tools) → Account Settings → Synchronization and Storage
Delete cached files taking up space:
C:\Documents and Settings\<profile>\Application Data\Thunderbird\Profiles\<profile>\ImapMail\*