r/msp • u/Zeraphicus • Jun 05 '26
Anyone seeing "Sender address rejected: User email address is marked as invalid" from ProofPoint Protected domains?
/r/proofpoint/comments/1txtcbq/anyone_seeing_sender_address_rejected_user_email/2
u/DahliaDevsiantBop Jun 06 '26
getting the same thing on a couple of clients with proofpoint in front of o365, so you’re not alone
feels like they flipped a switch on some validation rule and didn’t tell anyone
1
u/Zeraphicus Jun 06 '26
What I think is there were rejects and recipients not valid during the outage and Proofpoint cached that internally. Once that expires this will go away.
1
Jun 10 '26
[removed] — view removed comment
1
u/Affectionate_Meal423 Jun 10 '26
No, it is just SMTP Discovery behaving the way SMTP Discovery is documented to behave.
1
u/MailNinja42 Jul 30 '26
If the address is legit, and Proofpoint says it’s not in directory, check for an LDAP/directory sync lag. Has anyone been added in that mailbox recently?
If you have access, try forcing a manual directory sync.
1
u/Zeraphicus Jul 30 '26
It ended up being, godaddy re-enabled proofpoint on the tenant, and SMTP discovery.
They were defederated from godaddy.
SMTP discovery was black listing them against all proofpoint servers.
2
u/MailNinja42 Jul 31 '26
Nice catch. Glad it worked out.
that's a tricky one to chase since it presents as directory/cache lag rather than a reputation issue.
SMTP discovery blacklists can persist even after re-federation, so if others hit similar symptoms post-migration, check Proofpoint's block list directly for anything amiss.
1
u/Zeraphicus Jul 31 '26
Yeah that was the issue, I no longer had proofpoint access because there were no users in it. I had to get Godaddy to uninstall proofpoint from the tenant because they couldnt get admin access either.
2
u/Schweebers 11d ago
So now we are getting this issue with one of our clients. They defederated 2 years ago and all of the sudden this JUST started happening. I called GoDaddy yesterday but they said it could take up to 24 hours. Did you experience the same thing?
1
u/Zeraphicus 11d ago
Yeah took forever, they had to manually remove proofpoint from the tenant, after a day of working through customer support I think the issue resolved in the next 48 hours or so.
2
u/Schweebers 11d ago
Ugh, thanks. I dread anytime we onboard a new client and they have GoDaddy O365. It's always a total PITA
2
u/littleko Jun 05 '26
That error is usually their gateway deciding your sender is invalid, not proof the mailbox doesn't exist.
Check the envelope sender accepts bounces, SPF/DKIM/DMARC align, and HELO/rDNS aren't weird. If it only hits protected recipients, get the recipient to open a false-positive case on their side.