The 10053 mail error is very generic and is related to the other end of the connection, rather than with Kiwi Syslog Daemon.

Below are a few things that you might want to check:

1. Do you have a firewall installed, either software or hardware, that may be blocking the transmission?
   
2. Do you have any Anti-virus software that may be blocking the transmission. If you are running AV software then try disabling this, then testing the mail again.
   
3. Do you have a gateway server that has either a firewall or anti-virus software installed on it, which may be causing the issue.
   
4. Check with your mail server to confirm that this is not causing the issue, by dropping the connection.