421: User Exit rejects open for connection.
Explanation
The FTP server is running with the security user exit FTCHKIP. The user exit does not allow the IP address to access the FTP server.
System action
FTP continues. The client connection is rejected.
User response
Contact the owner of the FTP server to have the IP address authorized in the FTCHKIP user exit.
System programmer response
If necessary, update the FTCHKIP user exit to allow the IP address to access the server.