EXCLUSIVE

The NFL Network is responding to Heath Evans -- who claims he should NOT have lost his job for sending sexual pics to a wardrobe lady because she sent sexy pictures back.

But, the NFL Network ain't buyin' what Heath's sellin' -- essentially saying the fact it was mutual doesn't mean it wasn't "misconduct" in the first place.

"Heath’s employment was terminated as a result of his own misconduct – which he freely admitted to on Twitter today," network spokesperson Alex Riethmiller tells TMZ Sports.

"Before severing its relationship with Heath, the NFL carefully considered all of the circumstances, including the information that Heath provided. In the end, the NFL concluded that his conduct was not acceptable in our workplace and we stand by our decision to terminate his employment."