Error Code 421 – Host Not Reachable

Error Code 421 – Host Not Reachable

Error Code 421 – Host not reachable usually means the mail server (or remote host) you’re trying to connect to is not accepting connections.

Common causes:

  • The destination mail server is temporarily down.

  • A firewall or security setting is blocking the connection.

  • Network issues are preventing your system from reaching the host.

  • The server might be rejecting connections from your IP or mail provider.

In email systems, a 421 error is considered a temporary failure. That means the sending mail server will usually try again later automatically.

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