Finally got that damn web app to send out mails (2am). Turned out mail server worked, rails was properly configured, delayed jobs were running and were getting proper rights and environment. The issue was wrong configuration in app itself (somebody skipped part of the wizard). But still, fixing somebody's else server with webapp I know just a little about in languages I know even less about (not a web developer) after few guys failed and just within five hours, makes me feel both dumb (should have noticed much sooner) and proud (figured it out in the end).