%% You should probably cite rfc8461 instead of this I-D.
@techreport{ietf-uta-mta-sts-02,
    number =    {draft-ietf-uta-mta-sts-02},
    type =      {Internet-Draft},
    institution =   {Internet Engineering Task Force},
    publisher = {Internet Engineering Task Force},
    note =      {Work in Progress},
    url =       {https://datatracker.ietf.org/doc/draft-ietf-uta-mta-sts/02/},
    author =    {Daniel Margolis and Mark Risher and Binu Ramakrishnan and Alex Brotman and Janet Jones},
    title =     {{SMTP MTA Strict Transport Security (MTA-STS)}},
    pagetotal = 15,
    year =      2016,
    month =     dec,
    day =       15,
    abstract =  {SMTP Mail Transfer Agent Strict Transport Security (SMTP STS) is a mechanism enabling mail service providers to declare their ability to receive TLS-secured connections and an expected validity of certificates presented by their MX hosts, and to specify whether sending SMTP servers should refuse to deliver to MX hosts that do not offer TLS with a trusted server certificate.},
}