Thanks for all the advice on here. 
i'll do what I can to follow the positive points of focusing on my, DH's and DS's future, and not looking back.
Daily emails are kept extremely trivial - it's usually my father whinging about something trivial (we went out for lunch, your mother's coffee wasn't to her liking; we went to a concert, the venue wasn't good enough; some bloody teenager refused to serve me in a shop because I called her a stupid child... etc), me responding in bright & breezy fashion (oh well, at least the playing in the conecrt was good/ the rest of your meal was good/ there was another shop round the corner... etc). My mother hasn't bothered emailing me in years, and only did it infrequently in the first few years after I left - though she will respond to my sister's emails several times daily.
Bobbysgirl we have phone (Skype) contact once a week. My parents talk about themselves/ go off on rants about other people's stupidity & fecklessness etc. for an hour without drawing breath, then get off. They haven't asked about anything to do with our life in a long time - my father basically seems totally uninterested except when he can find a negative comparison to make with someone he deems "better" than me or DH - and my mother only wants to know so she can rub it in that I might not've heard from whoever she's asking about because they probably don't like me because I'm such a waste of space (no, I usually haven't heard from whoever it is because I last spoke to them 30 years ago in primary school...).
Jane10 you seem to have the insight into my parents' mindset that I lack. So what do you think they think about me? On the one hand you say I'm projecting, on the other you imply that my parents are probably right as we only have what I've said. If they have significant problems in their lives that make them too unhappy to respond positively to anything I do, then they do a pretty good job of hiding them in between living busy lives of apparently healthy privileged retirees with lots of fun activities, expensive overseas holidays, wide circle of acquantainces, etc. My mother's only terrible disappointment in life that she talks about (other than me) is that my father won't take her on a round the world cruise or buy her diamonds for her birthday.
They are certainly unwilling to engage. However everything points to that being because they think I'm a waste of oxygen and always have been, and they're embarrassed about me.
Need to look forward, not back. Off to fold some baby clothes and put up the curtains in DS's room...