Here's what's new in Thunderbird 1.5:

* Automated update to streamline product upgrades. Notification of an update is more prominent, and updates to Thunderbird may now be half a megabyte or smaller. Updating extensions has also improved.
* Sort address autocomplete results by how often you send e-mail to each recipient.
* Spell check as you type.
* Saved Search Folders can now search across multiple accounts.
* Built in phishing detector to help protect users against email scams.
* Podcasting and other RSS Improvements.
* Deleting attachments from messages.
* Integration with server side spam filtering.
* Reply and forward actions for message filters.
* Kerberos Authentication.
* Auto save as draft for mail composition.
* Message aging.
* Filters for Global Inbox.
* Improvements to product usability including redesigned options interface, and SMTP server management.
* Many security enhancements.

Windows
Operating Systems

* Windows 98
* Windows 98SE
* Windows ME
* Windows NT 4.0
* Windows 2000
* Windows XP (Recommended)

Minimum Hardware

* Pentium 233 MHz (Recommended: Pentium 500MHz or greater)
* 64 MB RAM (Recommended: 128 MB RAM or greater)
* 52 MB hard drive space