[otrs] Outbound email queue

Hello, I am using OTRS with SMTPTLS to send all email to an outbound mail relay (postfix) and this is working perfectly. However, I am unable to locate where the logs are being stored. Also, if by some chance my outbound relay isn’t operating as expected, OTRS does not appear to be queueing the emails the way I would expect (like postfix does). What is OTRS using to send mail? Can I make it use postfix? OS is Debian. -- John