email client <---> filter <---> SMPT server
Rather than connecting directly to mail.myisp.com, you connect to 127.0.0.1 and the filter then connects to mail.myisp.com
Your filter looks like an SMTP server to your normal email client, and looks like an email client to your ISP's mail server.
The filter sees everthing going back and forth, so it can then mess about with the messages as it sees fit.
Start simple with a "logger" filter which just dumps everything to a file, so you get the hang of it.
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Posting Sage
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since Dec 2005