Changing our domain - how it affects outlook/teams already installed

Hello,

thank you again for all the clarification.

About default domain - I need to have old email address reachable also after rebranding, so I will add "companyA" as an alias for each user mailbox. So I believe that with or without changing the default domain to CompanyB, emails sent to companyA should be received anyway? However, I plan to change default domain for sure - was just wondering whether there may be any unexpected impact as I will not be changing sharepoint domain at this stage.

About sharepoint - would you recommend any link to procedure to follow? I already have a plan, would however like to double check it against official MS recommended procedure and adjust if required.

I'm doing some testing these days, so may run into few other situations that I would like to confirm :) ... But for now, I'm should be fine. Would like to keep this post opened for few more days.

Dear Michal Sumega,

Good day!

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Thank you for your time and wish you a nice day.

Dear Michal Sumega,

Thank you for providing more details about your situation.

Regarding your first question, it is expected that users will need to remove their old email account and add the new one in Outlook after changing the primary email address. This is because Outlook caches the email address and settings, and it may take some time for the changes to propagate. Waiting longer may help, but it is not guaranteed to resolve the issue. Unfortunately, there is no way to centrally manage this process for end users, as it requires manual intervention on their part.

Regarding your second question, changing the "Default" domain in M365 admin to "companyB" is not necessary, but it can help simplify the management of email addresses and domains. If you keep using "companyA" as the default domain, users will still be able to receive emails sent to their old email addresses, but they will need to use their new email addresses when sending emails. If you change the default domain to "companyB", users will be able to use their new email addresses for both receiving and sending emails, and it may help avoid confusion.

Regarding your third question, you can change the primary email address for shared mailboxes, distribution lists, and groups in M365 admin by editing their properties. However, changing the "default domain" to "companyB" will not automatically change the primary email addresses for these objects. You will need to manually update them.

Finally, changing the SharePoint domain to "companyB" a week later should not cause any serious issues, as long as you follow the proper procedures and ensure that all users are aware of the change. It is always a good idea to test the changes in a non-production environment before making them in a production environment.

Let us know if you need any further help. I would really appreciate your cooperation and understanding.

Hello!

thank you for the details... great to have some confirmation/clarification on what I'm trying to accomplish :) ...Yes I expect to do some steps manually when switching to the new domain.

Just to explain further:

• we use hybrid scenario - and I will be configuring proxyaddress there to have the "companyB" as primary (SMTP:) and "companyA" as an alias (smtp:). I will do it for each user in AD as I can't do it in M365 (due to hybrid set up as it will not allow me to change it there)
• I have waited for about 12 hours from changing the primary name/primary address for my testing users and got the experience described above. What I was not expecting is that I would probably need to ask each user to remove email account from OUTLOOK and add the new one (same experience with OLD and NEW outlook). Not sure if this will be changed automatically if I wait longer? The other apps were ok and it is easy to sign out/sign in if needed.
• if manually removing old account and adding new account in Outlook is required, wondering whether there is a way to deal with it centrally to help our end users. I was thinking about deploying a profile via Intune, but I guess it will fail as I need to 1st remove the old one, and then add new one (as it reports me that the account/email is already added when was trying to manually add new account to Outlook while the old was still there)

I maybe have few questions and would be great to get some info about them:

• do I need to change "Default" domain in M365 admin to "companyB" as well? What will be the difference if I do not change it (and will keep using "companyA" as default), and if I change it to "companyB" please?
• is there a way to change primary name for sharedmailboxes, DLs, groups in M365 Admin? Or will changing the "default domain" to "companyB" change the primary email addresses for them to the "companyB" domain?
• I will be changing SharePoint domain to "companyB" a week later, I guess there will be no serious issues when doing it as a separate work (few days after emails)

Regards,

Dear Michal Sumega,

Good day! Thank you for posting to Microsoft Community. We are happy to help you.

When you change the primary domain in your organization, it can cause some disruptions in the Microsoft 365 apps. It's normal to experience some issues during the transition period. When you change your domain from "companyA.com" to "companyB.com", it will affect the email addresses of your users. The primary email address of your users will change from "@companyA.com" to "@companyB.com".

Regarding the email addresses, after changing the primary domain, all new emails sent from your organization will show the new domain "companyB.com" as the sender's email address. However, for the old emails, the sender's email address will still show the old domain "companyA.com" as an alias.

To ensure that internal emails are shown as received from the new "companyB" domain, you will need to update the email address of each user in the Microsoft 365 admin center. You can do this by going to the "Users" section, selecting the user, and then clicking on "Edit email addresses". To avoid confusion for the recipients, you can consider setting up a forwarding rule for the old email addresses to the new ones. This way, any emails sent to the old email addresses will be automatically forwarded to the new ones, and the recipients will only see the new domain in the sender's email address.

Regarding the Microsoft 365 apps, it's normal to experience some inconsistencies during the transition period. You may need to sign out and sign back in to the apps to ensure that they are using the new domain. If you continue to experience issues, you can contact Microsoft support for further assistance.

I hope this helps! Let me know if you have any further questions. Please understand that our initial response may not always resolve the issue right away. However, with your help and more detailed information, we can work together to find a solution. Thank you for your help.