i think i have the same question - i want mails to be sent from a different mailserver (smtp), not by using the local sendmail of the linux server and look for a way to configure that in dolphin.
(reason: regular abuse of the various websites on the server to send out spam, disallowing send as nobody has fixed it, but now dolphin cannot send anymore, as it sends as nobody and seems not to have any options to change to other mail servers))