Email::Valid does respect this considering such a mailbox specification
invalid. b06c6bc831cbb9e9eb82fd3ffd5a2b674cd940d0 addressed the issue, but
only if Email::Valid is available.
Signed-off-by: Uwe Kleine-König <ukleinek@informatik.uni-freiburg.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>