@misc{rfc6647,
    series =    {Request for Comments},
    number =    6647,
    howpublished =  {RFC 6647},
    publisher = {RFC Editor},
    doi =       {10.17487/RFC6647},
    url =       {https://www.rfc-editor.org/info/rfc6647},
    author =    {Murray Kucherawy and Dave Crocker},
    title =     {{Email Greylisting: An Applicability Statement for SMTP}},
    pagetotal = 17,
    year =      2012,
    month =     jun,
    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{]}},
}