It was a long shot and it didn't quite work.
I should know better but I was sort of hoping that getting the email hosting on the VPS to work would miraculously make the email portlet work too. It didn't. Having read some stuff on how to do it:
a) I can see why Liferay didn't have time in the day they spent installing 4.2
b) I can see that I'm not yet the kind of person I want trying to make it work
...because we need the portal user base to syncronise with the email user base which appears to require integration at the database level, etc. etc. etc. and getting a novice like me to do it is likely to prove dangerous and expensive.
Oh well. Must check the budget...