Mail It In Meaning

Example: Used other than as an idiom: see mail,‎ it,‎ in.
To deliver a performance without commitment or effort, with lackluster results.
2008 January 11, Bill Keveney, “Idol tries to get its groove back”, USA Today, page 1A:
  "I do think the judges mailed it in during Season 6, relative to previous years," Welton says. "Simon needs to be nastier. […] "
2009 January/February, Keith Bellows, “Go, But Go Green”, National Geographic, volume 26, number 1, page 22:
  So when you have to write two columns a week that are going to be read by a lot of people around the world, you can't just mail it in. You're thinking all the time.
2010 May 25, Joe Cowley, “Crunch time comes early; Sox 7 Indians 2; Peavy^s point: Next month is make or break”, The Chicago Sun-Times:
  Listen, we're not mailing it in, we're trying to get better.