Authentication Errors
- Error 403: access_denied
- Error 550-5.7.0: Mail Relay Denied
- Error: invalid_grant
- Error: Could Not Authenticate
- Error: Key Not Found
- Error: InvalidAuthenticationToken
- Error: Token Has Been Expired or Revoked
- ErrorSendAsDenied
- 401 Error: invalid_client
- Error: invalid_client: AADSTS7000222
- Error: Password Command Failed
- Error 503: Bad Sequence of Commands
- Error: 403 Forbidden
- Error 535: Authentication Credentials Are Invalid
- Error: SMTP Error 550
- Error 550-5.7.26: This Mail Is Unauthenticated
- Error: AADSTS700016: Application With Identifier Not Found in the Directory
- Error: invalid_grant: AADSTS700082
- SMTP Error 504: Timeout Error
- Error 454 4.7.0: Too Many Login Attempts
- Error 401: Unauthorized – No Valid API Key
- SMTP Error 533
- SMTP Error 530
- Error: 550 5.7.708 Service Unavailable
- Error: Could Not Open Socket
- Error 504-5.7.4: Unrecognized Authentication Type
- SMTP Error 471
- Error 513: Relaying Denied
- Error 535-5.5.4: Optional Argument Not Permitted for Auth Mode
- Error 412: Account Pending Approval
- Error 503-5.7.0: No Identity Changes Permitted