we use the same method as regular PB client: outlook ole or smtp, but we push everyone to use ole outlook primarily because of the SMTP limitations we have with encryption requirements and the licensing for the encryption object that works with smtp.  

in the future i will be looking into either using .net to send with SMTP (imported assembly into PB) or a REST api.  the new powerserver 2021 deployment will allow for more options since it will be mostly just powerbuilder.