Those users haven’t sended anything, that is the issue. If they would I had plenty of options and group messages is for me the most practically solution.
and back to the real problem. When an user buys a service they get link to a form created by a plugin in WooCommerce. No, I can’t use Discourse for that, because you know, they aren’t anykind users. I can send that form to Discourse, but only from from approved addresses, and customer’s addresses aren’t and won’t be approved in SES. So I need to connect that customer together that sended form, now a PM, somehow. Then I can continue with that customer in forum, because of all the tools it offers.