%% You should probably cite rfc7444 instead of this I-D.
@techreport{zeilenga-email-seclabel-07,
    number =    {draft-zeilenga-email-seclabel-07},
    type =      {Internet-Draft},
    institution =   {Internet Engineering Task Force},
    publisher = {Internet Engineering Task Force},
    note =      {Work in Progress},
    url =       {https://datatracker.ietf.org/doc/draft-zeilenga-email-seclabel/07/},
    author =    {Kurt Zeilenga and Alexey Melnikov},
    title =     {{Security Labels in Internet Email}},
    pagetotal = 14,
    year =      2013,
    month =     dec,
    day =       1,
    abstract =  {This document describes a header field, SIO-Label, for use in Internet Mail to convey the sensitivity of the message. This header field which may carry a textual representation (a display marking) and/or a structural representation (a security label) of the sensitivity of the message. This document also describes a header field, SIO-Label-History, for recording changes in the message's label.},
}