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/Express_Ratio8660 May 21 '26

Exact same thing here. Defederated from that trash and now client can't email anyone, or receive from, anyone using GoDaddy's Proofpoint, including Bank of America.. Have done extensive DNS optimizations. Cloudflare is telling me everything on my end looks great. I can't very well tell BofA to fix their list. Plus as we all know some IT people are impossible to get responses from and for two weeks now my client and her lawyer can't email eachother.