On Fri, Jan 31, 2014 at 12:41 PM, Vernon Schryver <v...@rhyolite.com> wrote:
> > You have records which absolutely > > need to be public: SPF, MXs--mail won't work otherwise. > > I hope I misunderstood the intended meaning or context of those words, > because their literal, context free meaning that SPF and MX records > are required by SMTP is wrong. > > SPF might be considered required by unsolicited or semi-solicited > bulk mail senders to help large scale "free" mailbox providers gauge > the legitimacy of mail advertisements. Otherwise SPF is *not* > required. As proof consider both this message and the DCC mailing > lists (i.e. old school solicited bulk mail.) In some cases SPF > harms SMTP delivery, especially when combined with DMARC. > > Because I'm in neither the email advertising business nor the large > scale "free" mailbox businesses, the only unambiguous use I've found > for SPF records is to try to prevent mail. I publish SPF RRs for some > domains that send no mail in order to reduce NDRs or "bounces" of > forged mail from bad SMTP servers (mail receivers) that fail to validate > SMTP Rcpt_To values during the SMTP transaction. > > > The case for MX records being required for SMTP is clear. In the > absense of an explicit MX record, the standards require SMTP clients > (mail senders) to infer an implicit MX from derived A or AAAA records. > > > Vernon Schryver v...@rhyolite.com > Indeed, the intent of my words was that SPF only makes sense if it's public--presumably you set up trust between your internal mail servers in other ways. It's not required for SMTP to work--plenty of domains don't use it. Thank you for the correction, Vernon. John -- John Miller Systems Engineer Brandeis University johnm...@brandeis.edu
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