On Mon, 5 Jul 2021 09:35:22 -0400 Greg Wooledge <g...@wooledge.org> wrote:
> On Mon, Jul 05, 2021 at 09:23:03AM -0400, Polyna-Maude > Racicot-Summerside wrote: > > Reporting-MTA: dns; premium58.web-hosting.com > > > > Action: failed > > Final-Recipient: rfc822;bjoern.ri...@greenbone.net > > Status: 5.0.0 > > Remote-MTA: dns; mail.greenbone.net > > Diagnostic-Code: smtp; 550 X-Host-Lookup-Failed: Reverse DNS lookup > > failed for 162.213.253.79 (failed) > > unicorn:~$ host 162.213.253.79 > 79.253.213.162.in-addr.arpa domain name pointer cyrania.com. > unicorn:~$ host cyrania.com. > cyrania.com has address 172.67.185.109 > cyrania.com has address 104.21.59.235 > cyrania.com has IPv6 address 2606:4700:3031::6815:3beb > cyrania.com has IPv6 address 2606:4700:3031::ac43:b96d > cyrania.com mail is handled by 0 _dc-mx.f1202d9a4fb3.cyrania.com. > > Your "reverse" (PTR record for 162.213.253.79) doesn't match. Which > is to say, none of the "A" results from cyrania.com. match the > original IP address of 162.213.253.79. > > Some SMTP receivers may care about that. Apparently the receiver for > greenbone.net (whose name is mail.greenbone.net) is one of them. > It's a pretty common requirement, as at one time it was the second best spam defence (after accepting mail only for named users). Not so good now that many ISPs are providing some kind of PTR record. But I haven't deleted the check from my mail server... -- Joe
