Mozilla's Thunderbird is a great cross-platform alternative for reading e-mail. I've found that the software can require some tuning to provide the best possible experience, though. Here's a tip to keep your Thunderbird install speedy and healthy: compact your mailboxes.
I've mentioned before my love for Thunderbird. Through its support for the POP3 and IMAP4 protocols, the program is compatible with nearly any messaging system, and its cross-platform nature makes it ideal for mixed-client environments. Like any love affair, though, ours has not been without its complications. I discovered that Thunderbird's Profiles directory could get really large, even when it seemed that it wasn't storing that many messages. After some investigation, I've found that the developers have built in a facility for keeping the program's disk consumption under control, and that's the "Compact Folders" command.The manual "Compact Mailboxes" command can be found under the "File" menu, but the most efficient way to accomplish regular cleaning is by having Thunderbird compact its mailboxes automatically. Follow the menu path appropriate for your platform, and check the appropriate box in the program's settings...
- Windows: Tools → Options → Advanced → Network & Disk Space → Disk Space → check "Compact folder when it will save over 100 KB" → click "OK."
- Mac: Thunderbird → Preferences → Advanced → Network & Disk Space → Disk Space → check "Compact folder when it will save over 100 KB" → click "OK."
- Linux: Edit → Preferences → Advanced → Network & Disk Space → Disk Space → check "Compact folder when it will save over 100 KB" → click "OK."
The fault comes from the message storage scheme that Thunderbird uses locally, the venerable mbox format. Mail messages are stored in a single text file for each mailbox. Deleted messages are flagged so they aren't displayed anymore in the mailbox view, but they aren't really removed from the mbox file until that file is compacted. The more messages you've read with Thunderbird, the larger your mbox files are. Every time you make a change to a mailbox -- deleting a message or moving it to another mailbox, for example -- your mbox files need to be rewritten. It's this process of rewriting large mbox files that can, over time, make Thunderbird seem laggy during mailbox operations. Making sure that your mbox files are compacted regularly will provide a better mail-reading experience for you and your users.
For more tips like this, you can check out the Thunderbird knowledge base at mozillaZine.