Related Clues:

• Initial request?
• Email command
• Confirm one's attendance
• Abbr. often following 23-Down
• Invite initials
• "Let us know," initially
• Evite letters
• Invitation abbr
• Letters of invitation?
• "We'd appreciate your answer," on invitations
• "Let us know if you're coming" letters
• Say you can make it, say
• Give feedback
• Decline, maybe
• Write back