Error Library SMTP Error 451-4.4.2: Timeout – Closing Connection SMTP Error 442: Connection Dropped During Transmission SMTP Error 451-4.3.0: Mail Server Temporarily Rejected Message Error: SMTP2GO E_ApiResponseCodes: ENDPOINT_PERMISSION_DENIED Error: cURL Error cURL Error 28: Connection Timed Out SMTP Error: Key Not Found SMTP Error: MailboxNotEnabledForRESTAPI Error 553 Sender Address Rejected: Invalid Sender Email Address SMTP Error 550 Host Unknown: Incorrect DNS Settings SMTP Error 550: Requested Action Not Taken: Email address does not exist SMTP Error 451: Temporary Local Problem: Temporary server problem SMTP Error 421: Connection Timeout: Network issues Error 534-5.7.9: Application-specific password required Error 535: Authentication Failed: Incorrect Login Credentials