Using Outlook for iOS for personal email and calendar management
Hello C. Matthew Peterson
Welcome to Microsoft Q&A forum. First, please feel free to check out AI answer
To help narrow this down, are you using the Microsoft Outlook app or Apple’s built-in Mail app, and is the address an Outlook.com/Hotmail account or a Microsoft 365 work account?
Please also sign in through Outlook on the web and try sending a test message. If webmail works, the mailbox itself is working and the problem is limited to the iPhone app.
If you are using the Outlook app, open Outlook > profile icon > Settings > select the account > Reset Account.
Please share any exact error message shown, you can send them here with your personal information removed or send it to Private Message that I have opened.
I'm waiting for your reply