The Al Capone of the Info Highway says:
A while back, there was a discussion about how to fake a from address by telneting into port 25 in a site. Many people discussed the pro's and cons, but I wanted to know if anybody knows of a way to stop people from getting in there to send the message in the first place.
Sure. Turn off mail to your site.
Beyond that, the store and forward nature of mail makes it impossible to stop this. The only real solution is to require digital signatures on all email.
Perry
Identd is pathetic, but may help with finding who did it. (Also, a good look at the mail headers will help too.) If the mail was a forgery on the local site, a check in the mail logs will do, as sendmail is not accessed when mailing from user@localhost to anotheruser@localhost. Enough of the "FAA's... the info that everyone knows, or should.". Other than using PGP or PEM, or writing a new RFC for mail, is there any other way to verify that a message is authentic that I missed?