What is Thunderbird?
Thunderbird is a full-featured e-mail and newsgroup client that makes emailing safer, faster and easier than ever before more.
Given the maturity of the underlying Mozilla code, Thunderbird is very usable. However, it is considered a Technology Preview, and as such is assumed to have defects.

What´s new?

Here are the highlights for this release of Thunderbird:

* Windows Installer

Thunderbird now comes with an installer for Windows making it easier than ever to start using Thunderbird!
* New Default Theme on Mac OS X

The new Pinstripe theme fits in with the look of Mac OS X.
* Improved Junk Mail Controls

The algorithm for the adaptive junk mail controls has been heavily redesigned to learn faster and catch more spam.
* New Brand Identity

To be consistent with the Mozilla Foudation's goal of brand identity, Thunderbird has a new logo and supporting artwork thanks to the fine work of the Mozilla Visual Identity team.
* Other New Features...

IMAP users can now benefit from support for the IMAP IDLE command which allows the mail server to push notifications such as new mail arriving as soon as it arrives.

Thunderbird supports server-wide news filters that apply to all newsgroups on a server.

Thunderbird includes Secure Password Authentication using a new cross-platform NTLM authentication mechanism for IMAP, POP3 and SMTP.

Mail filters can now mark messages as junk.

Offline support is an optional download component in the Windows installer and is no longer a separately-downloaded extension.

Mac OS X users now get new mail notification in the system dock.

The DOM Inspector is an optional download component in the Windows installer for theme authors.

Tools > Options > Compose > HTML Options allows you to set up default HTML compose options such as font, size and color.

Attachments can be opened directly from the compose window to verify their contents before sending.

Thunderbird now supports the notion of multiple identities per mail account. This makes it easy to have several e-mail addresses which end up going into the same account. Read More about how to set this up.
* Recently Fixed Bugs

In the case of a failure when copying a message to an online Sent folder, Thunderbird will now ask if you would like it to try again.

0.6 on Windows includes several improvements to Simple MAPI that allow it to work with older versions of Microsoft Office.

Pasting data from an OpenOffice.org spreadsheet no longer pastes random HTML garbage before the actual spreadsheet data into HTML compose.

Fixed several situations where LDAP connections were left open when using LDAP auto complete or performing searches on LDAP directories.

Improved view source behavior.

Mail notification for POP3 messages that are marked deleted or marked read by mail filters no longer occurs.

The "Mark All Read" keyboard shortcut now works for Linux GTK2.