Custom SMTP Errors for Office365

This article describes common errors with SMTP for Office365.

To set up custom SMTP, please refer to this article.

Fixing common authentication errors:

https://docs.microsoft.com/en-us/exchange/mail-flow-best-practices/fix-issues-with-printers-scanners-and-lob-applications-that-send-email-using-off#error-authentication-unsuccessful

Error:

Invalid login: 451 4.7.0 Temporary server error. Please try again later. PRX4

or

535 5.7.139 Authentication unsuccessful, the request did not meet the criteria to be authenticated successfully. Contact your administrator

Useful Articles/Questions:

Office365: Temporary server error. Please try again later. PRX4 | Blog | Limilabs

Sending Mail via Microsoft 365 Channel fails with 451 4.7.0 Temporary server error. Please try again later. PRX4

Fixing error-authentication-unsuccessful error

https://learn.microsoft.com/en-us/exchange/mail-flow-best-practices/fix-issues-with-printers-scanners-and-lob-applications-that-send-email-using-off#error-authentication-unsuccessful

Solution:

Customers need to enable SMTP Authentication for an account that’s used for sending emails

Enable or disable SMTP AUTH in Exchange Online