%% You should probably cite rfc4021 instead of this I-D.
@techreport{klyne-hdrreg-mail-05,
    number =    {draft-klyne-hdrreg-mail-05},
    type =      {Internet-Draft},
    institution =   {Internet Engineering Task Force},
    publisher = {Internet Engineering Task Force},
    note =      {Work in Progress},
    url =       {https://datatracker.ietf.org/doc/draft-klyne-hdrreg-mail/05/},
    author =    {Graham Klyne and Jacob Palme},
    title =     {{Registration of Mail and MIME Header Fields}},
    pagetotal = 54,
    year =      2004,
    month =     may,
    day =       11,
    abstract =  {This document defines the initial IANA registration for permanent mail and MIME message header fields, per RFC 3864. {[}STANDARDS-TRACK{]}},
}