I hereby join in, too.

Thanks, I didn't take into account that people might read this as an encouragement to randomly message people on Lesswrong. And thanks for giving me more clarity about the implicit norms here.

To clarify: The person likely found my mail address on my homepage, where it is exactly for the reason that I'm generally happy to be contacted by strangers.

Highly depends on your role and personality I guess.

As a community builder and someone pretty high on extraversion, I'm generally happy to add more people to my loose network. If there's just a bit of overlap between my and a stranger's interests, I expect there to be a far higher upside than downside risk to us knowing that the other exists and what they work on. Of course, I may change my opinion on this over time while my time becomes more valuable and my loose network larger.

Any generalizable rules you can think of about whom better not to cold message at all?

Paraphrasing is particularly useful for finding out whether you understood the other person correctly. For example, if a person says "I'm a cellular biologist.", you could paraphrase that as "You currently work in cellular biology. Right?"