unsend

From un- (“reversal”) +‎ send.

unsend (third-person singular simple present unsends, present participle unsending, simple past and past participle unsent)

1. (transitive, messaging, email, text messaging) To undo, cancel, or reverse the transmission of a message
   • 1997, Tom Lichty, ‎Jennifer Marx, ‎Jennifer Watson, The Official America Online Tour Guide - Page 61:

     To unsend a piece of mail, highlight the mail you wish to unsend and click the Unsend button.

unsend (uncountable)

1. (messaging, email, text messaging) The functionality or ability to reverse a message transmission

• Dunnes, sunned, unends