RFC 2368 <http://www.ietf.org/rfc/rfc2368.txt> specifies mailto: URLs as
having the following syntax:

     mailtoURL  =  "mailto:" [ to ] [ headers ]
     to         =  #mailbox
     headers    =  "?" header *( "&" header )
     header     =  hname "=" hvalue
     hname      =  *urlc
     hvalue     =  *urlc

The header fields in these URLs are roughly analogous to query
parameters in other URLs, but urlparse treats them as part of the path
(along with the email address):

>>> import urlparse
>>> urlparse.urlparse("mailto:foo@example.com?subject=hi")
ParseResult(scheme='mailto', netloc='',
path='foo@example.com?subject=hi', params='', query='', fragment='')

It should treat them as query parameters instead, which would not only
make it easier to access them but would also make it easier to access
the email address, since one would no longer have to parse headers, if
any, out of the path first.