* Improve exception class hierarchy
* Raise exception on malformatted "from_address" parameter instead of
yielding a negative verification result
* Add option to raise exceptions on ambiguous results
* Improve exception parameters to allow for a more structured analysis
of the negative response
* Yield a negative verification result upon the first permanent error on
RCPT TO, just like a mail server would also bounce after the first
permanent error
This unifies the tasks of splitting an email address into user and
domain parts as well as converting an international domain name into the
ASCII-compatible encoding (ACE).
Reinhard Müller
László Károlyi