What's Causing This Error
This error indicates that the client could not authenticate with the email server. It can be the cause of multiple reasons, for example:
- The user did not enter valid credentials when logging in.
- The user did not verify with the multi-factor authentication mechanisms enabled.
- The user did not have the correct SMTP settings configured.
Solution - Here's How To Resolve It
The user may follow the steps mentioned below to resolve the most common issues that could cause this error:
- The user must check if the credentials in use are valid.
- The user must make sure that they complete all multi-factor authentication challenges.
- The user must make sure that the client configurations contain the following valid SMTP configurations:
- SMTP server address
- TLS Port number (if applicable)
- SSL Port number (if applicable)