Default mail application
To set Gmail as the default mail application, go to "System -> Preferences -> Preferred applications" and set the mail reader to one of the following:
The easy way
Install gnome-gmail from http://gnome-gmail.sourceforge.net/ and Gmail will appear as a mail reader in the list.
Setting by hand
Set the following command as a custom mail reader:
bash -c 'sensible-browser "https://mail.google.com/mail?view=cm&tf=0&to=`echo %s | sed 's/mailto://'`"'
If the above doesn't work for you, as hasn't for some on 10.10, put the following in a script somewhere in your /home/username folder:
chromium-browser "https://mail.google.com/mail?view=cm&tf=0&to=`echo $1 | sed 's/mailto://'`"
then set the script's permissions to executable:
sudo chmod +x script.sh
then point preferred apps to the script.
This can also be done if you have Google Apps, with the following command (remember to replace example.com):
bash -c 'sensible-browser "https://mail.google.com/a/example.com/mail?view=cm&tf=0&to=`echo %s | sed 's/mailto://'`"'
To get notifications about new messages (and also a Launcher icon with unread messages count), install Unity Mail application:
sudo add-apt-repository ppa:mitya57/ppa sudo apt-get update sudo apt-get install unity-mail
See also this OMG! Ubuntu! post for details.