Related Clues:
- Letters directing letters
- Envelope letters
- Abbr. indicating to whom it may concern
- Ltr.-routing aid
- Letters that help a letter sorter
- To on a fax
- Opp. of "reverse"
- Mailers shorthand
- Letters on business letters
- Letter routing abbr.
- E-mail letters
- Bk. introduction
- Letter-routing abbr.
- Subject line starter on many an e-mail joke
- Envelope shortening