%% You should probably cite draft-ietf-sml-structured-email instead of this I-D.
@techreport{happel-structured-email-00,
    number =    {draft-happel-structured-email-00},
    type =      {Internet-Draft},
    institution =   {Internet Engineering Task Force},
    publisher = {Internet Engineering Task Force},
    note =      {Work in Progress},
    url =       {https://datatracker.ietf.org/doc/draft-happel-structured-email/00/},
    author =    {Hans-Jörg Happel},
    title =     {{Structured Email}},
    pagetotal = 11,
    year =      2023,
    month =     oct,
    day =       23,
    abstract =  {This document specifies how a machine-readable version of the content of email messages can be added to those messages.},
}