Related Clues:

• "Please answer"
• Accept or decline
• Inform the host
• Part of a prospective bride's pile
• Abbr. spotted in the mailroom
• Cover sheet abbr.
• Envelope or memo abbr., perhaps
• Say you'll go, say
• Mailroom abbr.
• Abbr. often before a name
• Ltr.-routing word
• Letters on an invite
• Farm-area mail rte.
• It may involve regrets
• Letters before a phone no., perhaps