421 4.5.2 - A mail transaction protocol command was issued which could not be interpreted, either because the syntax was wrong or the command is unrecognized. This is useful only as a permanent error.

Lookup for "421 4.5.2"

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 (4.5.2)

Syntax error

A mail transaction protocol command was issued which could not be interpreted, either because the syntax was wrong or the command is unrecognized. This is useful only as a permanent error.

SMTP Error Code: 421 4.5.2

Lookup for "421 4.5.2"

Basic Status Code Details (421)

Enhanced Status Code Details (4.5.2)

Syntax error