%% You should probably cite rfc6647 instead of this I-D.
@techreport{ietf-appsawg-greylisting-09,
    number =    {draft-ietf-appsawg-greylisting-09},
    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-appsawg-greylisting/09/},
    author =    {Murray Kucherawy and Dave Crocker},
    title =     {{Email Greylisting: An Applicability Statement for SMTP}},
    pagetotal = 17,
    year =      2012,
    month =     apr,
    day =       26,
    abstract =  {This document describes the art of email greylisting, the practice of providing temporarily degraded service to unknown email clients as an anti-abuse mechanism. Greylisting is an established mechanism deemed essential to the repertoire of current anti-abuse email filtering systems. {[}STANDARDS-TRACK{]}},
}