Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Hi Christopher Thompson
Greetings
Thank you for posting in Microsoft Community.
Generally when MFA is enabled for a mailbox, the number or email address added as the authentication method can only be accessed by the owner.
One work around would be to set an email address of a shared mailbox as an authentication method, then give the users that need to login to the email address permissions to the shared mailbox, however this is not very secure.
Granting the users delegate access to the email could be a better option as this email address can be added to their Outlook client, you may refer to Manage another person's mail and calendar items (microsoft.com)
Kind Regards,
Momo