Slang for doing the least amount of work possible or slacking off.
Hes really been mailing it in lately, he hasnt finished any of his labs.
by Runki March 15, 2005
To call out a co-worker for being lazy as it there last day.
"Tim you have really been mailing it in today, how about you actually get something done"
by Jahney November 02, 2007