Duplicate emails on two domains (.com and .co.uk)

Occasional Visitor



I'm in the process of migrating email from another service and I have three domains including a .com and a .co.uk. I'd like all emails to Email address removed to go to Email address removed


I know I could manually add aliases for each mailbox to include the .co.uk domains but that's a lot of work when my last provider let me use one domain as a mirror of another.


Any idea how to best do this in O365?



1 Reply
You can either use email address policy to add secondary email address to all the users.
Or you can just run one PowerShell command to update the secondary email address.

$AllMailbox = Get-Mailbox -ResultSize Unlimited
Foreach($A in $AllMailbox){
$NewEmail = $A.Alias + "@domain.co.uk"
Set-Mailbox $A.Alias -EmailAddresses @{Add=$NewEmail}}

If the alias is john and email address is "john @ domain.com". This will add an additional SMTP as "john @ domain2.co.uk"