Mason,

My linux box is my SMTP server. My ISP setup an MX record for me so that all mail to mobius-soft.com gets routed to my linux box. I use Postfix for my SMTP server. Among other things, it has a file called access, which it consults before it delivers mail. Whenever I get a SirCam attachment, I put the person's email address in this file with a reject code and error message. Then whenever they send me email, postfix bounces the email back to them with my error message. It's a manual process with having to add email addresses to the access file, but it's still better than a daily ritual of deleting 30 emails with SirCam from the same individuals.

Another thing I learned as a result of the MX record was that anybody could use my box to send mail. I quickly learned how to setup Postfix so only people with accounts on my linux box can use it to relay mail.