Issue with having exact same email address in both external email provider and M365 environment.

Copper Contributor

Hi, we have been using an external email provider for quite some time (example for the sake of clarity, e.g. me @ mycompany . com)


We needed Teams but not email service yet from M365, so I have claimed the domain (mycompany . com) but did not add any CNAME and MX records.  I created M365 users with the exact same name as in our external mail provider.


All was fine.  Teams is fine.  Email using external provider is fine.



Now we have a new company starting so I have also claimed another domain using the same tenant.  (For clarity this is called, company2 . com)


This company does not have an external provider, since its new, so this will be using M365 both Teams and email.


I added CNAME and MX records in the domain providers  It’s all done and fine.


Email from mycompany to company2, ok.

Email from google to company2, ok.

Email from any external client to company2, ok.

Email from google to mycompany, ok.

Email from any external client to mycompany, ok.

Email from company2 to mycompany, failed.


The mail did not go to the external provider.  Instead it went to the email with the same name in M365.  If I login OWA I can find that mail.


How do I configure so that the mail from company2 (same tenant) will go to external provider for mycompany?




1 Reply
Have you made sure that the account in the tenant with the mycompany domain have not been assigned an exchange license?