Firstly, thanks to everyone for the brilliant Virtualmin.
I have several sites on a Linode VPS and mail is sent through Postfix showing something like - li1234.members.linode.com (12.345.67.89).
There is no problem with this and it is as it should be.
However, is it possible to configure things so that Posfix mail is sent showing -
etc for each individual site?
EDIT - I should make it clear that this is only seen when recipients look at the source of their incoming email. From the point of view of the inbox, mail is received as Message Title from example.com as normal.
Many thanks again and best wishes.