SMTP Error Code: 421 4.1.6

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Lookup for "421 4.1.6"

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 (4.1.6)

Destination mailbox has moved, No forwarding address

The mailbox address provided was at one time valid, but mail is no longer being accepted for that address. This code is only useful for permanent failures.