How to change SMTP address, add old primary email address as alias. Do not remove all other alias

Question

Hi,

We have a new domain, and we want to achieve the following:

• Add the new domain as the primary SMTP email address
• We need to retain the old email address as an alias.
• We don't want to delete existing aliases and proxy addresses.
• The login also does not change. We want users to continue to log in using their old email address.
• We have an on-prem Exchange 2019 server, Hybrid. All mailboxes are in the cloud, but the domain controllers are still on-prem as the authority.
• We already registered the new domain, and I can achieve all this manually. I need to do this in bulk using CSV to ensure that only users who are in the CSV file will be modified to be cautious.

For this exercise, let's take John Smith as an example.

Username and login: JSmith

Current Email: ******@oldemail.com

New Email: ******@newemail.com

Proxy Addresses: there are multiple entries in Adsi edit for this user. SIP, FAXMaker, etc., that we want to keep as is.

How do I achieve this through Powershell or a free tool? I understand that there are many posts online, but I want to start new and ensure that this is custom to my request so I can follow. Thank you.

Answer 1

In Hybrid scenarios, you can easily address this by configuring an new email address policy: https://learn.microsoft.com/en-us/Exchange/email-addresses-and-address-books/email-address-policies/email-address-policies?view=exchserver-2019

If for some reason you are not able to leverage Email address policies, the "second best" solution is to use PowerShell. In particular, the -WindowsEmailAddress parameter of Set-Mailbox does exactly what you are looking for - it adds the new value as primary SMTP address, while preserving the old one as secondary. It does not change the UPN or anything else. Here's an example:

Set-Mailbox ******@domain.com -WindowsEmailAddress ******@newdomain.com

Answer 2

Thanks for your help. I haven't implemented it yet but thank you for your response. I will follow your suggestion.