1. Literally, to send something somewhere or to someone by mail. I mailed in the application months ago, but I still haven't heard from the university!

2. To perform a given task, duty, or activity with little or no attention, effort, or interest; to do something perfunctorily. Usually such a key player on the field, the team's star running back seems to be mailing it in this afternoon. I usually love his work in film, but he totally mailed in his performance for this voice-over role.