Toby Web Mail 0.4 is in the works. Changes include language customization (currently only available for English and Spanish — if you want to help out by translating a language file, e-mail email@example.com), better install and upgrade scripts, and a completely re-written message handling class. Attachment handling success is nearing 100%, and messages are now parsed into a standards-compliant format before they are written to the database, rather than every time they are displayed. Yay for optimization!
Update: Toby is no longer supported. I recommend using RoundCube Webmail instead.