si.Mail Alternatives

si.Mail

Published under GPL (you don’t have to pay for it if you are using it, full source code availability),
Localization,
Html message view,
MAPI, e-mail aliases support
Control downloading of images, executing scripts, using ActiveX contros in html messages,
Theme support,
POP3, SMTP, SMTP AUTH, IMAP*, NTLM support for both POP3 and SMTP(yahoo, hotmail,…)* access through plug-ins,
Multiple account support,
Preview mail on Server,
Automatic attachment compression,
Colorize possible dangerous extensions,
Remove of dangerous html tags before putting message to html viewer,
Multiple profile support under one Windows account(profile),
Plug-in support for importing and exporting of messages and address book,
Use anti-virus application to verify attached files before open/save
SSL & TSL connection,…
Use plug-ins and view / print attached files directly from si.Mail
store attachments in separate folder, so messages file can be smaller up to 33%
advanced message search
advanced pre-download, after-download and after-send filters
RSS, Atom feeds support
Minimize to system tray
Portable, just copy full si.Mail folder to USB stick and go with your messages anywhere
Automatic message classification (read description above) (can be disabled to lower memory consumption and make interface simpler)
Calendar and task management supported (can be disabled to lower memory consumption and make interface simpler)
+ a lot more, you can see some features with screenshots and description here

objects marked with * are not yet implemented