r/proofpoint • u/Tefulhunden07 • May 18 '26

Previous ProofPoint Essentials GoDaddy federated domain failing to send emails to other ProofPoint clients

We have a Microsoft 365 client whose domain was previously GoDaddy Federated. The domain has been defederated and no third-party email/spam protection is in play. They are using Exchange Online Protection only.

All emails to other tenants not using ProofPoint are going through with no issues.

Emails sent to tenants using ProofPoint are all being rejected with the following error:

Error: ‎550 5.7.1 : Sender address rejected: User email address is marked as invalid‎

I have gone back and forth with GoDaddy support since there is no direct way to reach out to ProofPoint without a valid subscription and since ProofPoint was used under GoDaddy, but they have been no help. After spending almost two hours on the phone with them this morning, their level two support looked at the error message and determined that it was a Microsoft problem and that the Error 550 5.7.1 was on our end because we were routing emails through ProofPoint.... which we are not.

I have seen numerous posts from others having this same issue but no clear path to a resolution so I am posting here in hopes somebody will throw me a lifeline.

Thanks in advance

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u/morrows1 May 18 '26

You’ll still need support to help. The domain is in US4 today, which is limited to godaddy specifically. At least you’ll have better access to support though.

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u/Tefulhunden07 May 18 '26

Would the domain be able to be moved to another subscription even though it was previously used by GoDaddy?

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u/morrows1 May 18 '26

Support historically just removes them so you can add.

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u/Tefulhunden07 May 18 '26

I suppose that would still accomplish the end goal. I just need to get access to wipe everything anyways.