Thanks to everybody for the responses. The winning solution was Ricks (see below) which worked like a charm after poking a suitable hole in my firewall.
Miark
[To listen to port 2525], in /etc/postfix/master.cf file, locate the lines that look like this:
smtp inet n - n - - smtpd -o cleanup_service_name=pre-cleanup
Add the following lines right after them:
2525 inet n - n - - smtpd -o cleanup_service_name=pre-cleanup
Then just do a 'postfix reload' and you should be in business.