"We all know an e-mail tax is infeasible,"
Do you not know how email works?
The tax would go to your ISP would would pass it to the consumer.
1 penny per 100 email. So not much at all.
I'm aware of how e-mail works down to the protocol level, but you can consider this my looking at the issue at a macro level. You can't work it into the e-mail protocol, for example, because e-mail is used the world over (very macro view). You can try to tax the transactions (e-mails sent), but how do you enforce this? Your suggestion of the ISP doing the taxing would work very well for anyone who uses their ISP's e-mail. But what about free e-mail services? Do they need to now charge the tax? Would free e-mail services become illegal? What if an American citizen uses an Australian-based free e-mail service? What if you and I have e-mail servers running on our home PC's and I send an e-mail to you? Would this be tax evasion?
I do relent that an e-mail tax could be feasible on a small level, but at the same time it would be easy to get around. Of course, most people wouldn't even know that there's such a tax, and it would be small enough and hidden on their bill that they wouldn't care.
" and sales tax for online purchases and for digital purchases are likely unavoidable forever,"
I'm one of those who do pay use tax, and I'm against too much taxation, but will admit that a national sales tax for online purchases would make it easier to ensure I'm not overpaying. As it is, I'm tracking whether I buy something from a seller within California or not within California or outside of California but big enough to be forced to collect sales tax...
" but here's hoping talk of taxing data usage doesn't work its way to Washington."
hmmm. I don't know. We may be in a situation where a tiny tax could go a very long way.
The problem here is, a long way to what? How likely is the money to be spent on something worthwhile, and how likely to be spent on something that's certainly a waste? (Not that this is any different than many taxes and fees we already see.)
Just my thoughts on it. Feel free to point out any flaws in my thinking!