While XenForo's mail queue system is nice for sites that use SMTP at the application level to send mail, I would guess that most sites don't do that, and rely instead on the normal MTA of the server (sendmail, Postfix, etc.), which is a mail queuing system in itself. So ultimately enableMailQueue defaulting to "true" means that most sites are using a mail queue at the application level to queue into the server's mail queue. For some reason I missed that XenForo was doing this, and finally figured out why there seemed to be a lag on mail XF sends out. Ultimately this was the fix: PHP: $config['enableMailQueue'] = false; So now it just queues into the normal server mail queue directly (queuing into XF's mail queue vs. the server's mail queue has no bearing on the user experience/speed).