Add a new domain as an alias to all of your Microsoft 365 accounts

A few days ago, while at a client site, I overheard a staff member recite his 31-character email address to someone over the phone, to say nothing of having to correct the other party. "No, it's singular architect. Mhm. a r c h i t e c t. Mhm. dot com."

I think you can see where I'm going with this. In fact, it's probably why you're here, so let get into it!

Environment: syncing Active Directory with Azure AD/Entra ID

Perform this step in your Azure AD/Entra ID environment

1. Buy your new domain and add it to Microsoft 365

Perform these steps in your AD environment

1. On a domain controller, open Active DIrectory Domains and Trusts
2. Right-click on the root container, called Active DIrectory Domains and Trusts and then choose Properties
3. Add your new, short domain to this list.
4. If you're unsure about the impact of running these commands in your environment, pause Azure AD Connect until you're satisfied with the new proxyaddresses values that this script creates.
5. Open PowerShell ISE and run:
   
   Import-Module activedirectory
   $proxynew = "@shortdomain.com"
   $users = Get-ADUser -Filter '*' -Properties SamAccountName, ProxyAddresses
   Foreach ($user in $users) {Set-ADUser -server yourdomainconroller -Identity $user.samaccountname -Add @{Proxyaddresses="smtp:"+$user.samaccountname+$proxynew}}
   ‍

1. Open a few AD accounts and confirm that the generated proxyaddresses are what you expect by going clicking the account's Attribute Editor tab, then scrolling down to the proxyaddresses entry. If you don't see an Attribute Editor tab, close the account window, then on the ADUC window, click View then Advanced Features.
2. Wait for Azure AD Connect to sync your changes, or force a sync by running
   
   Start-ADSyncSyncCycle -PolicyType Delta

Perform these steps in your Azure AD/Entra ID environment

1. Go to https://admin.microsoft.com
2. Open a user account and inspect the addresses under Aliases. You should see your new domain there. If not, open Synchronization Service where Azure AD Connect is installed and look for errors.

When I have the opportunity to add a new domain and add it as an email alias in a pure cloud environment, I'll update this post.