Heho,

hm, not sure. Looking at the 'email-security-scans.org' data, fcrdns is
at ~95.5% of senders. For comparison:

DKIM: ~55.2%
SPF & Valid: ~91.0%
TLS: ~96.0%
Greylisting (attempting to resend): ~97.4%
IPv4: ~97.9%
IPv6 (sending): 56.2%
IPv6 (sending+auth DNS+rec DNS): ~35.7%

So even though that sample is a bit biased, i'd say that fcrDNS is more
'lived practice' than SPF. ;-)

With best regards,
Tobias 

On Tue, 2023-05-09 at 11:40 -0700, Michael Peddemors via mailop wrote:
> Hi Laura,
> 
> I think we have to disagree here.  The PTR naming is set via
> SendGrid. 
> It doesn't NEED to be the same as the A record. This is for those
> MTA's 
> that do forward/reverse matching, which isn't always successful.
> 
> Yes, doing that for a IPv6 email address to satisfy Google, go ahead.
> 
> But nothing wrong with sending an email from a PTR with a name, that 
> doens't have the FQDN forward/reverse matched.
> 
> As long as there is a URL associated with the domain name.
> 
> eg. http://mileageplus.com (Redirect to UA site URL)
> 
> Perfect forward/reverse FQDN matching is still a little aggressive
> IMHO, 
> and especially problematic.  Some people think they need 20 PTR
> records, 
> one for each A record.. (No, that is worse)
> 
> Postfix does allow forward/reverse checking, I would NOT enable that
> for 
> the IPv4 space (yet)
> 
> On 2023-05-09 10:22, Laura Atkins via mailop wrote:
> > That’s a Sendgrid IP, they likely told UA to put in a DNS record,
> > but UA 
> > never did. ¯\_(ツ)_/¯ n
> > 
> > > On 9 May 2023, at 18:01, Stephen Frost via mailop
> > > <mailop@mailop.org> 
> > > wrote:
> > > 
> > > Greetings,
> > > 
> > > I'm getting some inbound email attempts that I believe are
> > > legitimate
> > > from United Airlines that are being rejected due to:
> > > 
> > > May  9 12:55:38 tamriel postfix/smtpd[1221960]: warning: hostname
> > > o1.email.smallbusiness.mileageplus.com does not resolve to
> > > address 
> > > 50.31.61.242
> > > 
> > > Tracking this back, near as I can tell, postfix is correct here
> > > in that
> > > 50.31.61.242 / 242.61.31.50.in-addr.arpa resolves to
> > > o1.email.smallbusiness.mileageplus.com but
> > > o1.email.smallbusiness.mileageplus.com doesn't seem to actually
> > > exist:
> > > 
> > > dig o1.email.smallbusiness.mileageplus.com a
> > > 
> > > ;o1.email.smallbusiness.mileageplus.com.IN A
> > > 
> > > ;; AUTHORITY SECTION:
> > > smallbusiness.mileageplus.com. 600 INSOA 
> > > vndcdf-fs0000-gma3-vip.ual.com. ualipconfig.united.com. 40 10800
> > > 3600 
> > > 2592000 600
> > > 
> > > Hopefully someone on here is from UA or knows how to get in touch
> > > with
> > > someone there who could like into fixing that.
> > > 
> > > Thanks,
> > > 
> > > Stephen
> > > _______________________________________________
> > > mailop mailing list
> > > mailop@mailop.org
> > > https://list.mailop.org/listinfo/mailop
> > 
> > -- 
> > The Delivery Experts
> > 
> > Laura Atkins
> > Word to the Wise
> > la...@wordtothewise.com
> > 
> > Email Delivery Blog: http://wordtothewise.com/blog
> > 
> > 
> > 
> > 
> > 
> > 
> > 
> > _______________________________________________
> > mailop mailing list
> > mailop@mailop.org
> > https://list.mailop.org/listinfo/mailop
> 
> 

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