Hello, i given a person ([email protected]) my e-mail ([email protected]) and he received back following message: This message was created automatically by mail delivery software. A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. The following address(es) failed: [email protected] (generated from [email protected]) host gmail-smtp-in.l.google.com [22.214.171.124] SMTP error from remote mail server after RCPT TO:<[email protected]>: 550 5.7.1 <[email protected]>: Sender address rejected: Common domain forgery (Log in to hide this advertisement) --- [email protected] e-mail is downloaded via POP3 by Gmail to my [email protected] Inbox I do not understand why that error happened, what can be the reasons. It looks like it is issue of the sender right? But i doubt about that. Or does google mean sender was [email protected] (which seems confusing). I doubt also about SPF record which may be missing on the mydomain.com hosting server, but unsure if it is taken into consideration, because mydomain.com is behind Cloudflare which also has DNS zone which contains SPF record: v=spf1 ip4:hostingserverip a mx include:mydomain.com ~all moreover for it to be even more complicated, the hosting server is in datacenter which is using some mail relaying system and they need to set their server hostname in all SPF records. Can their missing server in SPF record be the cause of the above mentioned error? seems strange, as it is just e-mail download, no sending out. EDIT: i have suspection this issue is caused by cPanel Email filters feature - simply the hosting account has feature which redirects e-mail matching rule to my gmail account, and i had it set for all mail. Unsure how this can trigger the "common forgery" error (if this is the cause).