Office365 - Adding alias for multiple users for custom domain

Question

Hi, my company is using Office365 under the Business Standard plan. We are using a custom domain as default, and we just added a new custom domain.
How can I create an alias for this new domain for all the active users ? Is there a way to do it directly when adding the new domain ? How about future new users : will we have to add manually aliases for each domains added ? Thank you

Answer 1

Unfortunately, you cannot automate this as Exchange Online does not support email address policies. Thus your best option is to use PowerShell. The solution will vary depending on whether you want to add the address as primary or secondary alias, but in both cases is fairly easy to do:

Get-Mailbox -RecipientTypeDetails UserMailbox -ResultSize Unlimited | % {Set-Mailbox -WindowsEmailAddress $_.PrimarySmtpAddress.Replace("tenant.onmicrosoft.com","newdomain.com") }

or

Get-Mailbox -RecipientTypeDetails UserMailbox -ResultSize Unlimited | % {Set-Mailbox -EmailAddresses @{add=$_.PrimarySmtpAddress.Replace("tenant.onmicrosoft.com","newdomain.com")} }

Make sure to replace the corresponding domain names, and of course, test against a user or two before running it across the company. Even better, expand these examples into a full-blown script with proper error checking and such. Here's one such example from Tony: https://office365itpros.com/2022/10/18/update-user-email-upns/