Crossword puzzle clue "important email marker"

Important email marker

Marker's marker

Marker-to-marker highway measurement

"I know this email is super detailed, but here's the important stuff:"

Subject heading for an important email

One with an important role in the production of a fantasy film or period drama (not so important for a porno, though)

I got mine in 6 minutes (using a felt marker)

Grave marker?