I found the case in which I have to send 1 email to several recipients. I have the names stored into a Sharepoint list.
Using REST API and a call into my Workflow I’ve been able to get a list of login names (using $expand=MyUserField and $select=MyUserField/Name), then you just need to concatenate them separate by ;.
At the end you should have a string that looks like domain\login_name1;domain\login_name2;domain\login_name3; into yout To field for the email.