@misc{rfc5231,
    series =    {Request for Comments},
    number =    5231,
    howpublished =  {RFC 5231},
    publisher = {RFC Editor},
    doi =       {10.17487/RFC5231},
    url =       {https://www.rfc-editor.org/info/rfc5231},
    author =    {Barry Leiba and Wolfgang Segmuller},
    title =     {{Sieve Email Filtering: Relational Extension}},
    pagetotal = 9,
    year =      2008,
    month =     jan,
    abstract =  {This document describes the RELATIONAL extension to the Sieve mail filtering language defined in RFC 3028. This extension extends existing conditional tests in Sieve to allow relational operators. In addition to testing their content, it also allows for testing of the number of entities in header and envelope fields. This document obsoletes RFC 3431. {[}STANDARDS-TRACK{]}},
}