O365 email stopped working!

[Koldov]

We have an old legacy O365 tenant that we have kept alive to catch any emails and forward them to our new GMail accounts.

 

These accounts are on 'Office 365 A1 Plus for faculty' and although I know these are being removed soon, they are currently all still licensed.

 

I have only kept select email accounts live (HT, BM, Finance, etc.) in case we miss any invoices or other important communications from anyone who hasn't updated their contacts/mailing lists or been informed of our new email addresses until we're fairly certain they are no longer needed. I know auto-forward is frowned on, but I have restricted sign-in and although I expressed my concerns, the HT said that even the LEA still send messages to the old email accounts even after repeatedly asking them to update their contact information for us, so they want them kept for now. 

 

Our BM asked me earlier this week, why he has not received an email (that needs to go to the old address before it can be updated). Although I'm no O365 guru, any log searches/email traces came back with all email activity basically dropping off a cliff on 03/11/2025 and nothing after that... 

 

 

I sent a test email from my GMail account to see if it got forwarded from O365 to their GMail and this was the reply: 

 

Delivery Status Notification (Delay)

Mail Delivery Subsystem <[email protected]>

Delivery incomplete

There was a temporary problem while delivering your message

Diagnostic-Code: smtp; 451 4.4.62 Mail sent to the wrong Office 365 region. ATTR35

 

I've tried to research what that means exactly, but I'll admit it's over my head. It basically says "The attempted mail delivery to Microsoft 365 used an MX record or smart host that contained an incorrect destination value for Microsoft 365." and about 'Smart Hosts', DNS and 'MX records', but I'm confused because I haven't changed anything...

 

 

[TheHyperTechie]

Are you using separate domains for Office 365 and Google? where do your MX records point?

Edited November 13, 2025 by HyperTech

[Koldov]

Just an update as  it now all appears to be working OK.

 

Checking our Domain in M365 Admin, showed an 'incomplete Domain setup'... not sure how as we've had it running for years! Interestingly I decided to complete the Domain set-up and it reported our MX records were incorrect!

 

 

It was expecting: 

Points to address or value - school-domain-co-uk.mail.protection.outlook.com

 

But it had: 

Points to address or value - 1234567890.mail.outlook.com

 

We don't deal with the DNS for this domain as it's legacy, so raised a support ticket and got a reply saying they've had a few of these lately and maybe Microsoft have changed something recently, or something they've changed has suddenly started applying...