Hello, > On Fri, Jul 23, 2021 at 09:44:38PM +0200, Thomas Walter via mailop wrote: >> Regarding RFC974 >> If the list of MX RRs is not empty, the mailer SHOULD try to deliver >> the message to the MXs in order (lowest preference value tried >> first). The mailer IS REQUIRED to attempt delivery to the lowest >> valued MX. Implementors are ENCOURAGED to write mailers so that they >> try the MXs in order until one of the MXs accepts the message, or all >> the MXs have been tried. >> >> It's been a while since I looked at this, but isn't "SHOULD" a >> recommendation? I understand this collides with the next "IS REQUIRED", >> but...? > > No, there is no contradiction. > > I could write a mailer that starts from highest preference value to > lowest. This violates the first "SHOULD", but fulfills the second > "REQUIRED".
Well it seems that RFC974 is deprecated and replaced by RFC 5321, section 5.1. "MX records contain a preference indication that MUST be used in sorting if more than one such record appears (see below). Lower numbers are more preferred than higher ones." So now this is not SHOULD, but MUST. So Microsoft violate (once again) a RFC... Regards, Xavier _______________________________________________ mailop mailing list mailop@mailop.org https://list.mailop.org/listinfo/mailop
