Mail (something) in phrase
To literally mean to send something to someone or to a particular place by mail
I mailed in the package. Have you received it yet?
To do something such as a given task, duty, or activity without much or any attention, effort, or interest
When being assigned to the role of the editor during the project, she totally mailed it in.
I feel like I'm not as interested in this job as I used to. All I do is just mailing it in.
The task is so easy that she can mail it in.
To send someone or something to someone or something else using a particular path
To send someone or something to continue forward.
The verb "mail" must be conjugated according to its tense.
The origin of this phrase is not clear.