A little program that lets me add a custom Reply-to: address to every email I send. This lets me know when someone gets hacked and lets me control spam.

More info here.. https://josh.com/notes/anti-spam-system/a2-rfc.txt

Install

I use this as a command line program under SmarterMail, but (for now) it only reads and modifies standard RFC5322 .EML files so should work with any email server if you can figure out how to set it up to call this on every outgoing email.

In SmarterMail you do this under Settings->General. You turn on command line program and put something like this as the command line...

c:\bin\sm-replace-replyto.exe %filepath "[email protected]" "Josh Doe <new-%[email protected]>" 53431184516 "g:/logs/"

...where...

c:\bin\sm-replace-replyto.exe is the full path to the executable to the program in this repo (you can get it from releases). Must have execute privileges.

%filepath is a fixed string defined by SmarterMail that will be repalced with the filename of the EML file in the spool directory by SmarterMail on each call.

"[email protected]" This is the "match" email address. It is a shared secret between you and this command line. The program will only process emails with this in the "Reply-to:" field, so the way you show the program that an email is really from you and that it should process it is by setting the "reply to" in your email program (Outlook, GMAIL, etc) to the same special value that you pass on the command line here. Otherwise it is not used for anything since the point of the program is to replace this with a generated address. Note that some email programs have restrictions on what kinds of addresses you can put in here, but it does not matter because you can put anything here as long as it is the same in both places.

"Josh Doe <new-%[email protected]>" This is a template for what the generated replyto addresses should look like. The %s is replaced with a 5 letter/number hash by this program.

"g:/logs/" This is an optional directory to write the logs into. Make sure it exists and has write, create, and modify rights. This is very handy to keep track of who got what addresses (see below).

Use

Once you are set up, anyone you send an email to will reply back to their special hash address. If you ever get a spam on one of these addresses, you can go look up who you gave that hash to and tell them that they got hacked.

To figure out who it was, goto the logs directory and search for the file with the name of the generated reply address (with .log at the end). Open this file and you will see a list of email address you ever sent that hash to and when.

Note that there might might be multiple people who got the same hash in case:

1. a hash collision (very unlikely)
2. You send an email with multiple "to:" people.

The multiple "to" problem

Unfortunately the EML file can not tell you everything about an outbound email. For example there could be a bcc which is not in the EML file.

Also, in the case with multiple recipients for a single email we currently just hash on the first email address.

Someday these problems will be solved by using the HDR file which has the actual delivery info in it, but for now this will have to suffice. I am just hesitant to do this becuase I can not find any documentation on the HDR file.