'a@b@c@d' quoted '"a@b@c"@d'
'a@b@c@d' quoted flags=8bitclean|bare_localpart '"a@b@c@d"'
'"a@b@c"@d' unquoted 'a@b@c@d'
'"a@b@c"' unquoted 'a@b@c'
'"a@b@c"@d@e' unquoted 'a@b@c@d@e'