Recent versions of sendmail have an interface called milter which allows you to test all sorts of things during the SMTP transaction. This makes it the natural place to add checks for things like forged e-mail addresses.

dvpmilter is just a wrapper around dvpquery which speaks sendmail's milter language. If it detects a forgery, then it will instruct sendmail to generate a temporary failure. Permanent (5xx) rejections are also an option, but I'm going for the light approach at the moment.

In the short time that this code has existed, it's already stopped something dubious. Some random box tried to send mail to me using a forged exploits.org user name. My secondary MX did the DVP check, noticed that it failed, and kicked back a temporary failure as intended. It obviously works.

Long story short: if you run sendmail and hate forged e-mails, I'd like you to check this out. If you run some other MTA and know how to write a plugin/add-on for it, that would also be helpful.