Is there a way to exchange contact data (for example the email address) with a user using a private channel? Sometimes I think that some user could become a friend and I don't know how to contact they. Of course this should only possible when the other user agrees.
standard offer: I make my email address visible in my profile, if you and the other person email me I can forward initial messages in both directions, then bow out once it is working. If you cannot see my address search on https://www.ams.org/cml/
Over the years, I have done this just a few times, it seems to work out.
Let's see: since I changed this to an answer, one may refer to this answer as part of the message (probably a comment addressed to the other party) suggesting the idea.
Saturday, 19 Sept.: that was different. Guy has a matrix question from a physics paper, not something I would be able to request. So he emailed me the paper as a pdf, I was able to confirm that his interpretation of the equation was correct, and I was able to answer the question. A question about positive definite matrix decomposition