It Won't Work!

The default response to almost all anti-spam email proposals comes in the form of a check list starting something like:

Your post advocates a

( ) technical ( ) legislative ( ) market-based ( ) vigilante ( ) form-based

approach to fighting spam. Your idea will not work. Here is why it won't work.
(One or more of the following may apply to your particular idea, and it may have
other flaws which used to vary from state to state before a bad federal law was
passed.)

( ) Spammers can easily use it to harvest email addresses
( ) Mailing lists and other legitimate email uses would be affected
...

You can read the full text of this variant of the anti-spam auto response.

Sadly, the response is usually correct. Email is ingrained as a simple, widely implemented, federated messaging protocol. Almost anything you suggest will break existing usage.

Oh dear.

We have to do something, though, and there are various means to try to identify spammers. Usually, because they don't follow the protocols -- although that leaves you at risk of rejecting email from legitimate organisations that don't follow the protocols either.