Sending, receiving, and organizing email in Outlook on the web for business
Hello Jake Harris2,
Thank you for reaching out!
Based on your description and error message, this is most likely related to depreciation of basic authentication. The deprecation of basic authentication will also prevent the use of app passwords for Exchange accounts. In this case, authentication will fail since SMTP or basic auth is disabled for your mailbox or email address.
A way around in this case would be reaching out to your M365/IT admin since they may have to enable SMTP Auth for your account or mailbox for this process. Enable or disable SMTP AUTH in Exchange Online | Microsoft Learn.
Thank you for your precious time and have a great day.
Best Regards,
Ashraf.