Logs for adding notes and replies?

One of our technicians swears he's sent replies to tickets, but emails are not delivered and notes aren't showing up. He asked me to watch him send a reply this morning, and naturally it worked. He says he had already sent two replies on that ticket, but they weren't delivered. They don't show up in the history of that ticket. I'm wondering if there is some sort of log elsewhere that I might check. He also says he's added Notes to tickets but they also sometimes don't show up. Could there be any sort of browser issue possibly interfering with functionality? He's on IE10.

Also, no Drafts appear, so it's not him hitting 'save' instead of 'send.'