I am almost there. Last night I (briefly) switched my router to deliver SMTP traffic to the new server.
My mail delivery works as follows.
1. mydomain.co.uk is hosted by one company who also manage the DNS entries.
2. I have created an entry for mail.mydomain.co.uk which points at my external static ip address.
3. I have set an auto forward for all mail to the domain to an address hosted by my ISP (firstname.lastname@example.org) - this is to give me an effective backup server.
4. My ISP then delivers all mail for %@myisp.co.uk to my static IP address by SMTP.
This works fine on my current server and I have compared the postfix settings between the two. The mail hits my server but then fails to get delivered. In this log entry the ip address is the external address for my router - i.e the static address for mail.mydomain.co.uk. I have set ispconfig to not publish DNS info. I have also created an entry in my hosts file 192.168.0.202 mail.mydomain.co.uk
Jun 19 09:09:57 deb-server postfix/qmgr: 39841E7D11: from=<email@example.com>, size=1433, nrcpt=1 (queue active)
Jun 19 09:09:58 deb-server postfix/smtp: connect to mail.mydomain.co.uk[nnn.nn.nnn.nnn]: Connection refused (port 25)
Jun 19 09:09:58 deb-server postfix/smtp: 39841E7D11: to=<firstname.lastname@example.org>, orig_to=<email@example.com>, relay=none, delay=35124, delays=35124/0.08/0.04/0, dsn=4.4.1, status=deferred (connect to mail.mydomain.co.uk[nnn.nn.nnn.nnn]: Connection refused)
I would appreciate any pointers on where to go from here.