It may my misinterpretation of how these files work. We had an issue where the C: drive fell below 4 GB of free space and the queue started rejecting external email. Obviously we shouldn't let the drive get that low on space, but someone overlooked the alert and it happened. In the future I will be running a scheduled script to clear out old IIS logs which will keep the drive in check.
But what I am trying to figure out is why email that wasn't being delivered, didn't end up being logged? Again, I may just be misinterpreting how it works. This is what I read.
"Reserve log files (Trnres00001.jrs, Trnres00002.jrs,...) Files that are used to reserve space for additional log files if the current log file becomes full."
I read a few other things, but what I was thinking it meant that if you fell below 4 GB of capacity, email will still be logged to those files and eventually be delivered once there is enough free space. That didn't happen. No email was logged. Also, nobody ever received a NDR saying their message wasn't delivered. So during the time frame that there was only about 3 GB of free space, no external email messages came through and nobody sending the messages knows their email was delivered. This obviously doesn't make management happy.
So how exactly is it supposed to work? I am guessing those log files are only used when the mailbox database logs no longer have capacity and not when the queue DB doesn't have enough space.