Advice on adding whitelisting to Mail mode

[J Krugman]

I recently read a booklet-length tutorial on Emacs Lisp, and now
I have a little project by way of exercise.  The idea is to add
whitelisting support to Mail mode.  "Whitelisting" is the strategy
of selecting the email messages one wants (and trashing or at least
quarantining the rest), instead of trying to stop the ones one
doesn't want.  The "whitelist" describes those messages one wants.
I want to add functions to Mail mode (and maybe RMAIL as well) to
simplify the process of maintaining a whitelist.  The whitelist
will be in the form of procmail recipes contained in ~/.procmailrc
(yes, OS == Unix).

I'm a bit uncertain on how to start this.  I've done a lot of
programming before, but I've never extended an Emacs mode, plus
this project entails parsing, modifying, and writing out a text
file, which I've never even seen done in Emacs Lisp.

Can someone point me to source code I can study to learn how to
structure my code, and how to do the basic tasks of
parsing/modifying/re-writing a text file?

BTW, if someone has already written the code to add whitelisting
support to Mail mode, I'd like to know about that too!

Thanks!

jill

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