Guideline for email setup scenario

I am searching for a tutorial/example/guide if there is one on sending
an email from a visitor (no user registration is needed currently) to my
site to someone else. The visitor has to enter their email address and
the recipient(s)' email address(es) in a form and submitted it to
generate the email. The tutorials I have seen so far demonstrate email
substituting email addresses in one case for another or there are more
setup requirements for my scenario (I would think so). Please point me
the way. Thanks!

You should be able to set this up by following the examples in
ActionMailer.

But even if you figure it out - don't do it. Even with good CAPTCHAs,
you'll end up being a spammer magnet. You'll also likely end up
sending mails that aren't likely to reach their recipients; if
foo@bar.com tries to send an email to his buddy baz@frob.com, here are
some issues:

- if bar.com defines an SPF record, your mail looks fake
- if bar.com DKIM signs its mail, your mail looks REALLY fake
- filters on frob.com that inspect the headers are going to be
confused

You may want to look into setting the envelope address to a real
address attached to your site, but it's still ultimately going to be
messy.

--Matt Jones