Others have addressed the technical complications of collecting an email tax, so I'll just note something about the SMS, in the UK at least.

It's hard to think of a proposal more guaranteed to destroy the image of the EU in the eyes of young people in the UK than to put a tax on the form of messaging that is central to their social lives.

Alain Lamassoure deserves a special medal for services to Euroscepticism for this proposal.