Crossword puzzle clue "letter without an envelope"

Letter without an envelope?

Answer to the riddle "What has rivers without water, forests without trees, and cities without houses?"

Letter that doesn't need an envelope or stamp

Letter abbr. that tells the reader there's something else in the envelope

Placed in an envelope along with the cover letter

Prepare a letter for an envelope

Love-letter envelope phrase

Sealer that might close a love letter envelope