Just saw your new thread, great idea, I hope people respond :)
I think I would panic a bit if something just turned up outside my front door from DD2 and DS mum. Not because she's any kind of threat - she's a lovely woman, and wouldn't harm them, but it's the potential that something might happen in the future. And added to that, DD2 would freak out, because whilst she loves her mum very much, her feelings are actually very complicated, and she needs contact to be done via a third party right now. I personally feel that having met their mum a couple of times, and written lots of letters etc, that I would be happy to write to her directly, but I would not be happy to arrange a visit with her directly. I feel I need a social worker to go between us before a visit. I hope that makes sense. I do understand why you wouldn't want social services involved, I do, and I understand the feeling that your mail is private. SS have sent back one letter I wrote after deciding it needed more positivity in it!
However, the reason they are there is for people like DD1. She got one letter, just one after adoption, and it wasn't vetted (old letterbox coordinator was crap) and it was just horrible :( I can't get over it even now, it made me feel ill and frightened. If they were to find out where we lived, it would be a disaster. As in, call 999 type disaster. The vetting service is there for a reason, and whilst you would never send a letter with anything horrible or undermining written in it, others would. And like Mary, i think it's a disgrace that anybody's confidential information gets given accidently to other people. Friends of mine got given confidential contact information for their childs first parent, and they were shocked by that. However, I also think people should be careful about what information is available about themselves. You found your sons parents via the public electoral role. I have taken myself off the public electoral role - whilst it's all very well to talk about facebook security and intenet security in general, there are easier ways of finding people if you have a name!!
I know you mean well, but they are probably frightened. I would contact them via the letterbox system when your next letter date comes up, but say to them that you didn't intend to frighten them, and won't call at the house again? All of us, adoptive parents included, have to have our letters opened and read - and we get ours sent back and get made to redo them if they aren't good enough as well, if it makes you feel better :) I wasn't allowed to write that DD2 had an official diagnosis of PTSD when she got it. Also had to put more positive things in the letter, etc. I know you have strongly expressed how you feel about your mail being read, but it's for your son - he will get a letter, and that will help him. I don't like the idea of my mail being read, but I do it for DD2 and DS, and I do it for their mum as well. I personally, like getting letters back - I would be upset if she didn't respond, and so would the children - and they matter the most in this