But:

The big problem with any penalty for spamming is finding the perpetrator. The technology behind email was designed on the basis of trust--the designers never imagined the problem of spam and just assumed that all mail was wanted. Thus, the email protocols are fundamentally very flawed and don't provide a way to control the flow of mail and catch spammers. You could specify the death penalty for spammers and it still wouldn't be much of a deterrent to people who know that the odds of getting caught are one in a million.

Since the problem arises from flawed technology, the solution will have to involve fixing it. It's too easy to fake the sender, so first of all the system needs strong identity control, probably in the form of digital signatures both for the people sending email and the mail servers handling the mail. This establishes a two-level chain of trust--a mail server whose identity is confirmed can then certify that each message it sends comes from a valid user of that system.

That would open the way for the best class of solutions I've heard proposed: Adding an economic basis to the email system.

Charge for email. Duh. With your regular and legitimate correspondents, the flow of pennies back and forth will tend to cancel out in the long run, or you could designate senders who can mail you without being charged. Senders of unsolicited mail will have to pay for the privilege, and when you consider that at a penny per message a typical spam campaign of a million messages will cost $10,000, the volume of spam will decline dramatically. Spam works now because it's a cheap way to sell cheap trash; when spam costs real money, it will be treated like any other advertising channel and its use will be restricted naturally to the more legitimate companies trying to peddle the more legitimate products. Thus, this scheme won't eliminate spam, but it'll sure as hell upgrade its quality.

Also, with identity control, it'll be possible to enforce spam regulations like the requirement to put "ADV:" in the subject line. All of a sudden your email program can eliminate 100% of the remaining spam just by keying on "ADV:".

It's probably not feasible, and perhaps not even just (though it's debatable), to execute spammers, but it is technologically possible to execute spam.