/
(?(DEFINE)
(?<addr_spec> (?&local_part) @ (?&domain) )
(?<local_part> (?&dot_atom) | (?"ed_string) | (?&obs_local_part) )
(?<domain> (?&dot_atom) | (?&domain_literal) | (?&obs_domain) )
(?<domain_literal> (?&CFWS)? \[ (?: (?&FWS)? (?&dtext) )* (?&FWS)? \] (?&CFWS)? )
(?<dtext> [\x21-\x5a] | [\x5e-\x7e] | (?&obs_dtext) )
(?<quoted_pair> \\ (?: (?&VCHAR) | (?&WSP) ) | (?&obs_qp) )
(?<dot_atom> (?&CFWS)? (?&dot_atom_text) (?&CFWS)? )
(?<dot_atom_text> (?&atext) (?: \. (?&atext) )* )
(?<atext> [a-zA-Z0-9!#$%&'*+\/=?^_`{|}~-]+ )
(?<atom> (?&CFWS)? (?&atext) (?&CFWS)? )
(?<word> (?&atom) | (?"ed_string) )
(?<quoted_string> (?&CFWS)? " (?: (?&FWS)? (?&qcontent) )* (?&FWS)? " (?&CFWS)? )
(?<qcontent> (?&qtext) | (?"ed_pair) )
(?<qtext> \x21 | [\x23-\x5b] | [\x5d-\x7e] | (?&obs_qtext) )
# comments and whitespace
(?<FWS> (?: (?&WSP)* \r\n )? (?&WSP)+ | (?&obs_FWS) )
(?<CFWS>