Mail bounces with “550 sender rejected” or a Return-Path mismatch. What now?

Receivers reject mail when the From address, the envelope sender (Return-Path), and the authenticated sending domain don’t line up, or when you’re sending From a domain you’re not authorised to use. We set the General Contact / Sales Rep sender addresses to a domain you control, align the Return-Path with your relay, and make sure SPF authorises the actual sending host. Once the envelope matches the authenticated domain, the 550 rejections stop.