What Ubuntu's plan to Mail client now that Mozilla dropped support of Thunderbird?
Mozilla has NOT dropped support for Thunderbird, they simply won't be adding any new features to it except security updates
Mozilla has only said that their developers will not be working on Thunderbird further, i.e. adding new features, etc after 20 Nov 2012. They will continue making security updates available for Thunderbird until 30 December 2013.
At the same time, outside developers ("the community") can continue working on a parallel version of Thunderbird (still released by Mozilla) which will include new features, etc.
Considering that Mozilla.org involvement in developing Thunderbird will stop only after Quantal is released, it's a little early to begin looking about for alternatives. Even if the community doesn't pick up the slack and Thunderbird begins to go obsolete, I'm sure that Canonical will have an alternative in place by the R-series (April 2013).
Judging by this blueprint currently targeted for the Quantal cycle, Mozilla's dropping of Thunderbird has caught people working on Ubuntu by surprise.
Default applications are usually discussed at Ubuntu Desktop Summits, and the next one is after Quantal is released. My guess is that Quantal may either ship with Thunderbird or switch back to Evolution (which was the previous default email client). This issue also affects the current 12.04 LTS, so this is likely to be brought up at the next UDS to offer a 12.04.x revision with a supported email client.
All of the above is speculative, of course.
Evolution is Seamless , try that.
And their is Unity Mail , it makes login available through Unity mail Application , but opens in Web Browser.
For Further officially available try this .
But currently in Alpha releases Thunderbird is Default Client.