Thunderbird

Thunderbird is Mozilla's solution to the e-mail client.

Earlybird is the "unbranded" version of Thunderbird.

Emerge
Emerging Thunderbird is a long process, a pre-compiled (binary) version exists for users who want a shorter install time:

Note that behavior of the pre-compiled version may be different in many ways including the choice of default applications for URLs.

XDG integration
To ensure Thunderbird is being used by other applications for handling  links, run:

External resources

 * Thunderbird tips and tricks (Mozilla).
 * Thunderbird on Mozilla's Forums
 * Thunderbird on Mozilla's Buglist