Connection Errors
- Error 451-4.3.0: Mail Server Temporarily Rejected Message
- Error: SMTP Error 543 – Routing Server Failure
- Error: SMTP Error 542 – Bad Connection
- Error 451-4.4.2: Timeout – Closing Connection
- SMTP Error 449
- Error: 442 Connection Dropped During Transmission
- SMTP Error 446
- cURL Error 60: SSL Certificate Problem
- SMTP Error 547
- SMTP Error 420: Timeout Connection Problem
- SMTP Error 453
- Error 523: Origin Is Unreachable
- Error 550-5.7.1: Unauthorized Email Rejection
- cURL error 56: OpenSSL SSL_read: SSL_ERROR_SYSCALL
- cURL Error 6: Could Not Resolve Host
- Error: SMTP connect() failed
- Error 502: Bad Gateway
- Error 421: Service Not Available, Closing Transmission Channel
- cURL Error
- cURL Error 28: Connection Timed Out
- Error: Could Not Connect to SMTP Host
- Error: Connection Refused
- Error: Resource Not Found