Scenario
After setting up Exclaimer, you notice that your email address has changed to the .onmicrosoft.com domain instead of your custom domain.
Reason
There can be multiple reasons why your email address has changed to the .onmicrosoft.com domain instead of your custom domain:
- Hybrid environment configuration issues: Changes or sync problems between on-premises Exchange and Microsoft 365 can cause email addresses to switch to the .onmicrosoft.com domain.
- Azure AD Connect misconfiguration: If Azure AD Connect isn’t set up properly, especially with the proxyAddresses attribute, email addresses may change incorrectly.
- Initial setup of third-party connectors: Running the initial setup for third-party connectors without properly configuring the proxyAddresses attribute can result in email addresses changing to use the .onmicrosoft.com domain.
- Verified domain changes: Changing the verified domain can trigger backend updates (ProxyCalc) that reset email addresses to the .onmicrosoft.com domain.
- Issues in pure Cloud environments: In purely cloud-based setups, issues can arise if the custom domain is not set as the default in the O365 admin center, affecting how email addresses are assigned and updated.
- Specific mailbox types or disabled accounts: Certain mailbox types or disabled accounts with incorrect SMTP settings can show the wrong domain.
Resolution
See the workarounds below to correct the proxy address issue and reset the email addresses; however, Microsoft recommends contacting their support for further assistance with this matter.
Check user proxy addresses in On-Premises Active Directory
To check user proxy address in the On-Premises Active Directory:
- Open the Active Directory Users and Computers (ADUC) console.
The ADUC tool is available on domain controllers or workstations with the Remote Server Administration Tools (RSAT) installed. - Open the View menu and check if the Advanced Features option is selected. This option allows you to see additional properties of user objects, including the Attribute Editor tab.
[PA: screen] - Navigate through the directory tree to find the user account you need to check. You can also search to find the user.
- Right-click the user account and select Properties.
- Select the Attribute Editor tab.
- Scroll down the Attributes list and select the proxyAddresses attribute. Verify that the user's primary email address is correctly listed with the company domain. In some cases, secondary email addresses, such as aliases may also appear.
Setting all Proxy addresses using PowerShell
To update proxy addresses for all users in Active Directory, you can use PowerShell to automate the process. This ensures all email addresses are set correctly, especially when making bulk changes.- Launch PowerShell as an Administrator.