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Currently, people who are open to receiving communication from other users are able to list an email address and other channels in their profile.

Anyone on HN can opt-in and does not require administration by the HN moderators. Or additional development effort by HN programmers.

Good luck.

Yes, and a few rare users do that.

However, I don't know that users that don't do it are 100% against being contacted by other HN users.

It's possible they're just hiding their email to prevent the usual marketing spam (my own position).

the usual marketing spam

Probably why there is no DM.

The OP question is about wanting to DM others.

Not about wanting to be DM’d.

DM would be what is called an “attractive nuisance.”