Correctly setting the return path on emails sent by PHP
Email commonly includes the sender’s address in two places. The From
header in the message body is the one that most people are aware of, and this is the address that email recipients see. However, the sending mail server also adds a Return-Path
before the message body. Recipients don’t generally see this address, but it is important for two reasons. First, it is used in a number of anti-spam checks. Second, it’s the address that typically receives non-delivery reports if a message can’t be delivered for any reason.