Code review

Main things

+<form method="get" action="<TMPL_VAR LISTSUBSCRIBEACTION>" id="listsubscribeform">

This should have ESCAPE=HTML (see HTML::Template). The other TMPL_VARs probably should too.

The method should be post, and the CGI should ideally not respond to GETs (because sending email isn't idempotent).

Minor things

It would be good to have the documentation specify exactly what "API" it expects from the mailing list: in this case it seems to be an address to which you can send a blank message with the desired subscription address in the From: header. I believe that works for most but not all mailing list managers (hopefully the ones where you're meant to mail the posting address with "subscribe" in the body have died out by now).


Might be better to have a separate parameter for the human-readable name?

+       my $list_subscribe_form = template('listsubscribeform.tmpl');

I wonder whether this would benefit from an optional template parameter, with this as default?

  'my supercool mailing list': supercool-subscribe@neato.great

This won't be available to websetup, which doesn't understand hashes/dicts/maps. If it was a list of flat strings with a syntactic structure, like the language list for po, then it would be. Sorry, I can't think of a particularly good syntax...