Related Clues:

• Aid for an early head count
• Supervisors drop serious summons from The Party requesting answer
• Use an SASE, perhaps
• It may contain regrets
• Counter provides option for those answering letters
• E-vite request
• Click yes or no on an e-vite, say
• Evite request
• Letters on a wedding invitation
• "Kindly let us know," on invites
• Answer an invitation, for short
• Evite notation
• 'Yes' after 49-Across, if all goes well
• Reply to the invite
• Counter option for those answering letters