Office365 – 451 4.7.0 Temporary server error. Please try again later. PRX5

A Chilkat user is getting this error response from smtp.office365.com. He successfully got his OAuth2 access token, but then when trying to send the email, the Office365 server responded with this error indicating a temporary problem: “451 4.7.0 Temporary server error. Please try again later. PRX5 …”

This is not an error caused because of the Chilkat implementation.

Some temporary condition on the server is preventing the email from being sent. Unfortunately, the error message is not helpful in knowing the reason.

One thing to remember is that an access token is only valid for short amount of time. Typically 1 hour.
You’ll need to refresh the access token if you haven’t already done it.
But I would expect a different error message for an access token that expired.

The “PRX5” is an internal error code used by Office 365 to identify the specific nature of the problem. The exact meaning of the “PRX5” code may vary and is not publicly documented by Microsoft. It likely refers to an internal process or subsystem within Office 365 that encountered a temporary issue.