I am using a dedicated server in a data center. as you suggest home based servers are problematic in that it is difficult to get the Reverse Name set up.
As it transpires a few days ago I followed up (yet again) with the company that was blocking.
this time I got someone who understood and did some real investigation at their end.
as if by magic, emails from my server are now getting through. they decided to add the server IP to their whitelist.
and it’s been good all week so far.
I could go and use an email service provider but I should be able to send mail (as long as I have the right setup in Postfix and enure I am not on a blacklist (mxtoolbox.com is heavily used ;o) )
thanks for those that input to my question and offered help.