This question is a followup to this previous question of mine. Let me quickly summarize. I'm a Physics PhD student interested in one particular subfield which appears to be very active and promising. I have studied some key papers about the subject and I do understand them, but I really don't know how to start doing research on the topic. I asked if I could remotely propose some kind of remote collaboration with some postdoc working in the subject to learn and gain experience and by the answer I get that it is indeed OK to do it.
This question is about how to do it so to maximize the chance of success. I know about one postdoc that has several important papers published in the subject. I watched one talk he gave online and he seems very approachable. Moreover in his talk he showed very clearly that there are lots of things to be done in the field.
That said, I would like to send him a message and ask if I could collaborate with him remotely. What I want is to get involved in the research in this fied, help and gain experience.
A first point is that he doesn't know me, nor do I know anyone who knows him. To be honest I don't know anyone who knows people working in the field.
In that scenario, what is the best way to propose such collaboration and how much information should I send with my message?