%% You should probably cite rfc7505 instead of this I-D. @techreport{ietf-appsawg-nullmx-01, number = {draft-ietf-appsawg-nullmx-01}, 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-nullmx/01/}, author = {John R. Levine and Mark Delany}, title = {{A NULL MX Resource Record for Domains that Accept No Mail}}, pagetotal = 6, year = 2014, month = may, day = 21, abstract = {Internet mail determines the address of a receiving server through the DNS, first by looking for an MX record and then by looking for an A/AAAA record as a fallback. Unfortunately this means that the A/ AAAA record is taken to be mail server address even when that address does not accept mail. The NULL MX RR formalizes the existing mechanism by which a domain announces that it accepts no mail, which permits significant operational efficiencies.}, }