Good linux email client for editing moderated posts?

Hi;

I run a majordomo list where a persistent disruptive individual had to
be banned.

Rather then moderating every post I used the taboo_body tag to bounce
emails with certain phrases in it.

This has been very effective.  However about once every two weeks a
mistake happens creating the need to "approve" a post.  For various
reasons having the server owner implement a perl script as suggested in
the docs is not going to happen.

I need to use an email client that will let me insert "From:" and other
headers to make "approved" posts look as they would have looked if they
did not bounce.

Can anyone recommend such a client?  My only requirement is that the
client should run on at least gnu/linux.  If it has a low learning
curve that would be a bonus, but not a requirement.

Thanks much in advance for any info.

Steve