Filtering is easy. Run pi-hole.
Original Message From: postfixlists-070...@billmail.scconsult.com Sent: February 14, 2019 12:44 PM To: postfix-users@postfix.org Reply-to: postfix-users@postfix.org Subject: Re: Click tracker removal ideas? On 14 Feb 2019, at 11:27, Phil Stracchino wrote: > Quick question I hope: > > Does anyone have any suggestions for a tool for filtering out click > trackers from links in email bodies and rewriting the links without > the > click tracking? I gather from your other messages in this thread that by "click tracker" you mean URLs that point to one host which redirects the user to another URL. It's important to understand that this has entirely legitimate uses and isn't reliably detectable without chasing every URL in a message, which may effectively mimic the end user doing something that they would not do themselves. So at the highest level of not breaking anything that is harmless for the end user, this CANNOT work universally and/or harmlessly. At the technical level, aside from the problem of breaking DKIM, this also would require decoding messages if they are encoded in quoted-printable or Base64 and create a permanent support load of identifying and interpreting all "click tracker" URLs. It's not as if there were some standard for how to write an URL which will ultimately cause a redirection in a manner that makes the ultimate endpoint discoverable just by picking apart the original URL. So at the technical level, you can't do it safely or reliably because people running redirection systems often don't want anyone picking apart their mechanics and will happily modify how they encode final destinations to resist de-obfuscation. So even though you shouldn't try it because it will hurt your customers and can't even do it well if you tried, the obvious tool framework for this would be a milter or a content filter that uses the Postfix SMTP proxy mechanism. If you're good with Perl, MIMEDefang (a milter) would be the obvious choice, since its interface is a set of stub Perl subroutines that let you do whatever you can write code for with a message and its metadata at the various stages of the SMTP transaction. But don't. It would not end well. -- Bill Cole b...@scconsult.com or billc...@apache.org (AKA @grumpybozo and many *@billmail.scconsult.com addresses) Available For Hire: https://linkedin.com/in/billcole
