SMTP Error Code: 421 4.7.9

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Lookup for "421 4.7.9"

Temporary Error - This status code indicates a transient issue and may resolve itself.

Basic Status Code Details (421)

Service not available, closing transmission channel [This may be a reply to any command if the service knows it must shut down]

Enhanced Status Code Details (4.7.9)

Authentication mechanism is too weak

The selected authentication mechanism is weaker than the server policy permits. Client should retry with a new authentication mechanism.