Reading email content is a different problem altogether technically and legally - so it's not a valid comparison. That's not what inspect means [1] packet attributes, ports for POST/GET, headers and routing are typically the data inspected. If Starbucks wanted to block or log how many people are hitting a GMail IP, however then yes that is their prerogative.

That said if you're doing email over bare HTTP then you're broadcasting that data publicly over RF anyway.

[1]http://searchnetworking.techtarget.com/definition/stateful-i...