Why did Thunderbird replace Evolution in 11.10?

Here's a list of pro's and cons on deciding to change to Thunderbird: https://blueprints.launchpad.net/ubuntu/+spec/desktop-o-default-email-client

Evolution pro's:

• Good integration with the desktop already (eg, messaging menu and appmenu)
• Integrated with existing translation infrastructure for developers in launchpad
• Calendaring functionality by default, and integrated with the desktop
• Support for syncing contacts with U1
• Contacts sync with GMail
• GNOME release process is better aligned with our 6 month cycle
• Exchange support (no idea how well this works, but it exists)

Evolution con's:

• Outdated and confusing UI
• Historically has been fairly slow and unstable (although it is better now)
• UI is pretty bad on netbooks and other small form-factor devices
• I'm not convinced that Evolutions additional features are that important to our target users

Thunderbird pro's:

• Responsive and more active upstream
• Familiar brand for users moving from other operating systems, which has the same benefits as shipping Firefox
• Lots and lots of extensions, and a very rich extension framework
• Initial account setup is so much more intuitive
• I like the tabbed interface ;)

Thunderbird con's:

• Translations not integrated with Launchpad (we have the same issue with Firefox though)
• Integration with the desktop lacking (no messaging menu or appmenu)
• No exchange support (not true for lightning: there is a working lightning data provider, http://gitorious.org/lightning-exchange-provider/pages/Home )
• Calendaring support is only available via an addon (Lightning), and is not integrated with the panel clock
• No GMail or U1 contact sync (although GMail contact support is available via an addon)

And adding all up the result is in favor of Thunderbird it seems.

Here is the the pdf 'Thunderbird & Evolution User research findings' on which they based the conclusion to change.

On canonical Thunderbird & Evolution Usability Testing

Canonical did a usability testing between both email clients to see which is more friendly to the user. Results can be seen at Canonical’s design blog.

Both Evolution and Thunderbird are great applications. The fact that Ubuntu will switch to Thunderbird as a default mail client, should not be considered as a discouragement from using Evolution. It'll be just as available, easily installable and well supported.

But setting up an email account is much easier with Thunderbird and that's important. It's also easier to use in many ways. And I've been an Evo-freak and spent several years living in it, so to speak, but I really love Thunderbird as an email client. It has some features Evo just can't compete with, in my humble opinion.

Another thing is that Thunderbird is also well supported on Windows and since we're now getting Ubuntu One support on Windows, I think it'll be nice to be able to sync contact data and bookmarks with both operating systems (and others in the future). For people who dual boot, for instance, this is magnificent. They'll just install LibreOffice, Firefox and Thunderbird in Windows, along with Ubuntu One, of course and then they can just reboot and still have their files, tools and other data just as available. The same goes for people who take their work home, such as students or office workers. Interoperability is key if Ubuntu is going to really hit the masses, and using Thunderbird as default helps in that regard as well as making Ubuntu easier to use.