Added 2nd Domain to O365 account

siringo

Client had 2 businesses, A & B, each had a seperate O365 tenant.

B folded and A took on their staff and require those staff to retain their email address from company B.

I removed the domain from B's O365 tenant and added it to A's O365 tenant. The B domain is listed in A's O365 account as healthy.

Everything looks OK, but I get errors when I send email to company B staff email addresses, which I've setup in O365 as email aliases.

This is the error:

ME1AUS01FT015.mail.protection.outlook.com rejected your message to the following email addresses:
xxxx@yyyy.com.au (xxxx@yyy.com.au)
Your message couldn't be delivered because there is a partner connector configured that matched the message's recipient domain. The connector had either the RestrictDomainsToIPAddresses or RestrictDomainsToCertificate set.
For more information about this issue, see DSN code 5.7.1 in Exchange Online - Office 365.
ME1AUS01FT015.mail.protection.outlook.com gave this error:
TenantInboundAttribution; There is a partner connector configured that matched the message's recipient domain. The connector had either the RestrictDomainsToIPAddresses or RestrictDomainsToCertificate set [ME1AUS01FT015.eop-AUS01.prod.protection.outlook.com]

The client uses a 3rd party anti spam service that I had to create inbound and outbound connectors for. I suspect this error is something to do with this service as it is only configured to work with company A's domain name and not company B's.

But as my Exchange knowledge is slowly slipping into the dark abyss of the back of my brain, I'm not 100% sure?????

Any help is greatly appreciated.

1337

I think the key here is RestrictDomainsToIPAddresses and RestrictDomainsToCertificate.

These are filters set to limit from what server emails (identified by IP or TLS certificate) can be sent for a specific domain.

1337

TenantInboundAttribution says that the problem is inbound so perhaps check the settings on the inbound connector. The connector has to allow the 3rd party IP/domain.

Maybe this will help:
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siringo

@Pete-S thanks for the help mate, I'm off to bed for the night, I'll check it tomorrow.

dbeato

Also you can setup a Cross Tenant Migration which I just did for 3 accounts into one, works well.
https://docs.microsoft.com/en-us/microsoft-365/enterprise/cross-tenant-mailbox-migration?view=o365-worldwide

You can also setup your Domain B on that AntiSpam System as well too.

siringo

Got this sorted out. In the end it was just a few simple changes that the 3rd party anti spam people had to put in place.

Thanks everyone for the help.