FYI, if you have been using the iOS Mail app before signing up for MFA, there is a chance the HUC account in Mail will stop working after registering.
Symptoms of this are repeated prompts for password to access your HUC account in Mail. This problem occurs because the Mail app was not designed with MFA in mind. You can get it working, but a couple of steps may be required.
1-Restart your phone. This might resolve the issue, and get the Mail app to properly communicate with the MFA process
2-If a restart did not resolve the issue, you will need to remove the HUC Email account from your iPhone / iPad.
3-After removing the account, re-add your HUC account to Mail.
Choose “Exchange” account type, server name outlook.office.com.
You should be prompted to sign in with your credentials.
DO NOT choose the “manual” option that appears during the setup process.
If you have registered for MFA, you should receive an MFA authentication prompt to complete the setup process.