%% You should probably cite rfc6710 instead of this I-D.
@techreport{melnikov-smtp-priority-20,
    number =    {draft-melnikov-smtp-priority-20},
    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-smtp-priority/20/},
    author =    {Alexey Melnikov and Ken Carlberg},
    title =     {{Simple Mail Transfer Protocol extension for Message Transfer Priorities}},
    pagetotal = 27,
    year =      2012,
    month =     jul,
    day =       3,
    abstract =  {This memo defines an extension to the SMTP (Simple Mail Transfer Protocol) service whereby messages are given a label to indicate preferential handling, to enable mail handling nodes to take this into account for onward processing.},
}