Sendmail restrictions and frontends

[Matthew Hawkins]

First of all, you might like to look at using postfix instead
(http://www.postfix.org/)

I'm not sure why you think that making sure your mail server is not an
open relay is some "over & beyond" measure, its out of the box
functionality with postfix and any other decent MTA.

You get finite control over who can send mail and where to, and can
apply header and body checks against mail.

As for a front end, it depends what map type you're going to use to
build your lists of allowed domains - postfix supports berkeley db, dbm,
regexp, pcre, ldap and mysql (and possibly others, eg cdb with patches)
It'd be simple enough to build a CGI that can modify any of these, do a
sanity check and issue a "postfix reload" if all's well.

-- 
Matt