Replacing onmicrosoft

GBMCMonty You can use the "bring your own email" wizard in the Teams Admin app or M365 Admin Center to connect your existing email to M365 and Teams.
 

Here's where you can find the wizard in your Teams Admin app:

If you don't have the Admin app, you can install it here: https://teams.microsoft.com/l/app/b47c7387-2807-440c-9fc2-7c8f46147a20?source=app-details-dialog

If you'd like to do the setup manually, you can see instructions here: https://learn.microsoft.com/en-us/microsoftteams/connect-teams-essentials-to-email

Lastly, don't forget that small business customers can access free customer support form Microsoft to help with setup tasks like this: https://support.microsoft.com/en-us/office/business-assist-for-microsoft-365-37deb8fe-61cc-4cf9-9ad1-1c8d93475070