@
@@
@a.
@..
@.@.
!
a!
!b
a!b
!@
a!@
!b@
a!b@
%
a%
%b
a%b
%@
a%@
%b@
@@
a@@
@b@
a@b@
a%b@
a%b@MYHOSTNAME
a!b@MYHOSTNAME
a@b@MYHOSTNAME
a[b]@MYHOSTNAME@MYHOSTNAME
a[b]%MYHOSTNAME@MYHOSTNAME
a[b]%MYHOSTNAME%MYHOSTNAME
MYHOSTNAME!a[b]@MYHOSTNAME
MYHOSTNAME!a[b]%MYHOSTNAME
MYHOSTNAME!MYHOSTNAME!a[b]
user@dom.ain1@dom.ain2
user%dom.ain1@dom.ain2
dom.ain1!user@dom.ain2
user@[1.2.3.4]@dom.ain2
user%[1.2.3.4]@dom.ain2
[1.2.3.4]!user@dom.ain2
user@localhost.MYDOMAIN
user@[321.1.2.3]
user@1.2.3
user@host:port