Acknowledgements
I would like to thank Pick Internet and HarmonyLogic for funding the development of this program and for alpha testing. I would also like to thank Gladesoft for feedback and keeping me honest in coding the program and for running a beta test version of this program.
And now, on with the show …
X-Grey is a standalone daemon that implements a greylisting policy
that any MTA can use.
Currently in production use at Pick
Internet, it has cut the spam volume by 90% (on those domains that are
currently employing its use).
Features of X-Grey include:
- Fast. It can handle around 6,000 sustained requests per second on a 2.6GHz machine. When tested on a 120MHz 486, it peaked out to 380 requests per second. It's fast because everything about the server is stored in memory.
- Configurable. You can have everything greylisted, or only mail from one particular server, from a particular sender to a particular recipient. Or anything in between. Email can be accepted, rejected or greylisted based upon the IP address, sender email or recipient email.
- Dependable. Configuration changes can be made while the server is running, so you never have to shut it down. If the program ever crashes, it will restart itself, picking up where it left off.
- Flexible. It currently supports Sendmail and Postfix, and extending it to support other MTAs is not hard.
- Networkable. (“Networkable”? Is
that even a word? Have I fallen to the forces of Marketingspeak?)
Have more than one email server? It can support multiple MTAs (even different types)
across a network (although it can work over the Internet, it's best
to keep an instance of
X-Greyon a local segment). - Boundable. It consumes a predictable amount of memory and disk space and expired tuples are automatically purged from the system on a periodic basis.