It's not something I have heard of before, but from some quick Googling it looks like it might be logs of some sort that your server attempted to mail to someone but was not able to do so... maybe...
Have you a vanilla Sentora installation or is it highly tweaked/modified?
Maybe a cron job that is trying to email system info to a sys admin but never being able to?
I'm really not sure. I'll see if I can find anything else out about it, and if I do, I'll post back here.
Hopefully someone else who knows exactly what it is might be able to help you stop it!
Keith
EDIT: Are there any clues in your postfix logs to suggest something is trying to send out these logs - if that's what they are?
Have you a vanilla Sentora installation or is it highly tweaked/modified?
Maybe a cron job that is trying to email system info to a sys admin but never being able to?
I'm really not sure. I'll see if I can find anything else out about it, and if I do, I'll post back here.
Hopefully someone else who knows exactly what it is might be able to help you stop it!
Keith
EDIT: Are there any clues in your postfix logs to suggest something is trying to send out these logs - if that's what they are?