%% You should probably cite draft-ietf-acme-email-smime instead of this I-D.
@techreport{melnikov-acme-email-smime-00,
    number =    {draft-melnikov-acme-email-smime-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-melnikov-acme-email-smime/00/},
    author =    {Alexey Melnikov},
    title =     {{Extensions to Automatic Certificate Management Environment for end user S/MIME certificates}},
    pagetotal = 4,
    year =      2017,
    month =     jun,
    day =       7,
    abstract =  {This document specifies identifiers and challenges required to enable the Automated Certificate Management Environment (ACME) to issue certificates for use for email recipients that want to use S/MIME.},
}