Callback verification
TECHNIQUE USED WITH SMTP TO VALIDATE E-MAIL ADDRESSES
Callout verification; SMTP callouts; SMTP callout
Callback verification, also known as callout verification or Sender Address Verification, is a technique used by SMTP software in order to validate e-mail addresses. The most common target of verification is the sender address from the message envelope (the address specified during the SMTP dialogue as "MAIL FROM").