Mail rejection stats for our external mail gateway
April 27, 2011
In my recent spam filtering stats, I noted that some spam was rejected before it made it to the spam tagging and filtering system. Well, here's some stats on roughly that; specifically, on how much email our external mail gateway rejects at SMTP time for various reasons. The numbers here are for almost the same seven day time period as the previous stats; there is about a six and a half hour difference in coverage due to when the two systems roll their logs (one does it at midnight, one does it at 6:30am or so).
So, over seven days we:
The two surprises that stand out in this are how frequently spammers
attempt to forge email as from our own domains and how many relay
attempts there are. I'm not terribly surprised that unresolvable
I'm not going to try to estimate the additional 'real' spam volume here,
because in part it depends on your assumptions. For example, should we
consider all email rejected due to unresolvable
(General information on our spam filtering is in CSLabSpamFiltering. While that was written in 2007, almost nothing has changed since then in our setup although I'm sure that the Sophos PureMessage people have been evolving it madly. Such is one of the benefits of outsourcing most of your anti-spam system.)
* * *
Atom feeds are available; see the bottom of most pages.