Okay, once a week or so I send a newsletter out to about 12000 people. I recently also adjusted my firewall to log a little differently as a result I have noticed some interesting activity in my logs. After sending the newsletter there have been thousands of DENIES to port 113 from remote systems, it seems this in reaction or as a result of the newsletter send, but why would they be trying to connect to my Ident port? I don't even have that port open in anyway, does sendmail use that port for some reason?
I also noticed some new sendmail log entries that look like this:

sendmail[11318]: fAJGND111315: fAJGPW011318: DSN: User unknown

I have never seen DSN used by sendmail at all, is it just a new warning format or something?

Thanks!
Mike.