Error Library Error: Email Sending Limit Error: Connection Refused SMTP Error: ErrorSendAsDenied Error 452-4.5.3: Domain policy size per transaction exceeded SMTP Error 447 Error 400: Invalid_request SMTP Error: Invalid_request: AADSTS50194 SMTP Error 521: Server Does Not Accept Mail SMTP Error 450: Requested Mail Action Not Taken: Mailbox Unavailable Error: Gmail Could Not Authenticate SMTP Error 554: Transaction Failed SMTP Error: MessageRejected (client): Email Address Is Not Verified Error: Gmail cURL Error 77 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
