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. Normally, /var/log/mail, or wherever syslog puts the mail.* entries. See /etc/syslog.conf. 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). Working as designed. A MTA does queuing, not the application. What is OTRS using to send mail? Can I make it use postfix? OS is Debian. Consider using something a little less weird than postfix (exim comes to mind) but yes, that's the desired setup. See https://otrs.github.io/doc/manual/admin/3.2/en/html/email-settings.html for details for at least one version.