I've had several clients ask this, and I've never been able to get or give a satisfactory answer. Can you (practically) put a working form into an HTML email?
My understanding is that you can, but that there's no guarantee of email clients properly handling it, so that method would only be practical with individual recipients that you'd had a chance to test with, rather than with huge mailing lists of people using diverse email clients. But my understanding comes from a lot of developer friends shrugging at the question and no authority that I've found giving a clear answer either way.
What does Stack Overflow think? What's the best answer when you're asked to do this by a client who, for instance, wants a few hundred people to fill out a survey?
(Don't bother just answering "provide a link to a form on a website". That's the obvious answer. I want to know specifically if there's a consensus about forms in email.)
1. HTML in email is perceived by some to be a blight
It just hardly ever works, and when it does work, it doesn't work properly.
I recently experienced a case where a rather lengthy html email, although well composed and worked rather well, was cut in half and prematurely trimmed by GMail ( due to length ) which mangled the design a bit.
I've also had cases where the HTML was so malformed the email turned up in my inbox as if it were really a blank email.
2. I don't trust forms in my email
For security reasons mostly, some clients may intercept the form action, and the post action won't go anywhere ( Especially in cases where they have a physical email client, Open Web browser and posting data via it, thats rather complicated ).
You are simply better off having a form on a website that you can control, and people don't have any nasty surpises about ( Especially if you need javascript to execute the form, many email clients won't put up with that )
Maybe, you can put a form in, but for the sake of sanity, be as backwards compatible as possible, so that somebody with a text based browser like Pine or Mutt can still read it, and be given a link to a working form that doens't require client magic.