Issues with Office 365

I’ve setup mailinabox on a new “Sacrifiicial” Domain

I’m using external DNS (as cloudflare free doesn’t support external dns servers)

i can send from office 365 to/from the mailinabox sacrificial domain with no issues.

However. I’ve now moved an existing domain (Migrated from gmail) to mailinabox.

DNS was setup exactly the same for this domain (exported the file from MIAB.

I can send email from MIAB to Office365, but replies - or new emails to the user both get the error

Your message to colin(at)OLDGMAIL Domain

couldn’t be delivered.
colin wasn’t found at OLDGMAIL Domain

More Info for Email Admins
Status code: 550 5.1.10

Could you be more specific. You can send from MIAB, but you cannot recieve?
Which server gives the 550 5.1.10

What is your Admin Status page saying on your MIAB?
Any errors?

Status page for the 2nd Domain here

Error message is coming from the Exchange 365 mailbox - either if i send directly to the email address

or if i reply to an incoming email from MIAB


This issue is with Office365 Exchange Online.
I am not an expert but it seems you have to make a connector to enable sending to an external domain. Are you able to send from MIAB to e.g. gmail and respond from there? This seems exclusivley an Office365 problem.

If you are the Office365 Exchange admin, a hint could be something like this:

the office365 account is one that i’ve had/used for 4 years

its been used for sending to multiple different types of mail systems.

I’ve just tried sending from a personal domain on gmail to this - and it got through - but the reply from MIAB back to gmail has gone missing.

I think i’m going to delete the external dns entries. and reinstall MIAB.

this is all preparatory work before i move my main email domain anyway :frowning:

You have no PTR record (reverse DNS) on the MIAB.
Also be ware that your entire block is listed under UCEPROTECT level 2. Do not worry if the IP is listed under Level 3, there is no cure for that except to change your cloud provider. Better change your region with no Level 2 listings. There are some IPs in France, Canada, Norway and the UK which are clean (NO RED). But definitely release and renew this one.

Your cloud provider is AS16276

The mail you send from MIAB to gmail maybe lending in SPAM.
After setting the PTR record check your IP or IPs on the multi blacklist check and remove yourself from as many as you can.

Check if outlook has your IP on their blacklist

Then start testing. Outlook maybe blocking you because you have no PTR.
Do not set the external DNS before everything is OK in the status page. Then move your records to an external dns if you wish.

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