Email extractor accepts strings like "John@epfl.ch@" as a valid email
address

scala> EMail.unapply("John@epfl.ch@")
res78: Option[(String, String)] = Some((John,epfl.ch))

which is unexpected and likely incorrect. 
As well it looks inconsistent with a treatment of "@John@epfl.ch" as
non-email

scala> EMail.unapply("@John@epfl.ch")
res80: Option[(String, String)] = None

Note: This is a good point, but too much for fixing in a reprint. Will
look at this for the 4th edition.