This guide helps you resolve an email error of the type "535 5.7.0 authentication failed".

Troubleshooting Authentication Failed Errors

The email authentication service on the servers may experience an issue for a few brief seconds in exceptional cases, for example, during unusual events on the infrastructure.

If a 535 5.7.0 authentication failed error occurs:

• Wait a few minutes and then try sending the message again; it should go through this time.

If the problem persists, check the points in this other guide.