l had hoped letterbox would help my son understand he wasn't rejected by his birth family and that he hasn't been forgotten about. I hoped it would also give him the opportunity to ask any questions he may have about his birth family
These are very big hopes you have for letterbox contact and I think you need to be prepared for the fact that these will not be fulfilled.
Your son has been rejected by his bio family, otherwise he wouldn’t be with you. You need to come to terms with this, so you can help him do so when he’s old enough to learn the words for what he has lived through.
I hope he’s not been forgotten about, but I don’t think you can rely on continued letterbox contact to prove this to you and him. It very often stops because the BF stop making contact, as Ted says. You need to be prepared that this might fail AND he’s not been forgotten about But he and you may ever have the proof of this.
It’s also very unlikely that he will be able to get answers to any questions he might ask about his bio family through letterbox. Even the most innocuous questions, such as likes and dislikes, sports hobbies etc , don’t usually get an answer.
If you hope that he will get answers to the big questions most adoptees REALLY want to ask, then you will surely be disappointed.
I know that you want to make everything ok for him. Perhaps you want to have a happy adoption story to tell him. That’s only natural but it’s not realistic in most cases.
I’m not writing these things to be harsh or criticise you, but to encourage you to work through your own feelings of disappointment and loss so you are free to help your son deal with his own feelings, whatever they are.
Otherwise you can end up pushing your own agenda on him , so he won’t fel able to share his feelings with you and will lock them up inside himself. Which I’m sure you don’t want .