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

[tkerby]

Hi

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?

Thanks

[#2]

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"