@ @@ @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