What does 454 mean?

SMTP 454 indicates temporary authentication issues:

What it means:

The authentication or encryption handshake failed temporarily. The server may require TLS and could not establish it. Credentials may be temporarily unverifiable.

Common causes:

TLS negotiation failure: Encryption setup did not complete. Certificate issues: Temporary certificate problems. Authentication backend down: Server cannot verify credentials.

Typical message examples:

"454 TLS not available" "454 Temporary authentication failure" "454 Try again later"

Response:

Retry with standard backoff. Check your TLS configuration if persistent. May indicate issues on receiving end.

454 is a handshake problem. The introduction could not be completed, but try again.