Exact response pattern
354 Start mail input; end with <CRLF>.<CRLF>InfoGenericProtocol
What it means
The server accepted the envelope and is ready for the message content.
Likely causes
- Normal DATA-stage response.
Recommended response
- Transmit the message and terminate it correctly.
Operational rule: Preserve the complete SMTP response, remote hostname, sending IP, envelope sender and timestamp. Never diagnose from the three-digit code alone.