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We are using Google Workspace and set Email forwarding using recipient address map to forward messages at our domain name (@example.com) to an external domain name (@external.com). Ex. mail sent to info@example.com will forward to info@external.com.

The forward works when we email info@example.com from one of our Google Workspace accounts - it goes to info@external.com.

When we email info@example.com from an external service like Outlook, we get the following error:

Message not delivered There was a problem delivering your message info@external.com. See the technical details below, or try resending in a few minutes.

Reporting-MTA: dns; googlemail.com Received-From-MTA: dns; someone@outlook.com Arrival-Date: Sun, 10 Apr 2022 23:36:01 -0700 (PDT) X-Original-Message-ID: XXXXX@XXXXXXX.namprd02.prod.outlook.com

Final-Recipient: rfc822; info@external.com Action: failed Status: 5.0.0 Remote-MTA: dns; mxw.263.net. (XX.XX.XXX.XXX, the server for the domain external.com.) Diagnostic-Code: smtp; 520 ip and spf record not match Last-Attempt-Date: Sun, 10 Apr 2022 23:36:08 -0700 (PDT)

RBT
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user1822824
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  • I’m not posting an answer because I’m not sure of the best solution. But the problem is that when mail is forwarded like this, your mail server becomes the IP address that is sending the mail, and that IP address is not authorized by the original service that sent the mail. That is an SPF failure. It’s a well known issue. That one reason why SPF failures alone cannot be used to block email reliably. Senders should also use DKIM to authenticate their mail. Your forwarding mail server needs to rewrite the “return-path” header to not break SPF. i.e. it should be info@example.com. – Appleoddity Apr 11 '22 at 13:07

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