That A record was only up there for 5 minutes, LOL, I was redoing the zone file and mistyped then when checking realised \i had made a booboo there and redid it. Must have been then that it was picked up. (It was very late)

Here was the error message
bombay.duck12@btinternet.com>: host mx.lb.btinternet.com[213.120.69.89]
    refused to talk to me: 421 re-prd-rgin-002.btmx-prd.synchronoss.net Service
    not available - no PTR record for 85.119.84.35

<bea.jay@ntlworld.com>: host mx.tb.ukmail.iss.as9143.net[212.54.56.11] refused
    to talk to me: 421 mx4.tb.ukmail.iss.as9143.net
    mx4.tb.ukmail.iss.as9143.net MXIN108 Failure to determine Reverse DNS for
    your IP 85.119.84.35. Fix or retry later.
    ;id=e02ZnsEO3k7hk;sid=e02ZnsEO3k7hk;mta=mx4.tb;d=20220411;t=214936[CET];ipsrc=85.119.84.35;

<joyron.b@ntlworld.com>: host mx.tb.ukmail.iss.as9143.net[212.54.56.11] refused
    to talk to me: 421 mx4.tb.ukmail.iss.as9143.net
    mx4.tb.ukmail.iss.as9143.net MXIN108 Failure to determine Reverse DNS for
    your IP 85.119.84.35. Fix or retry later.
    ;id=e02ZnsEO3k7hk;sid=e02ZnsEO3k7hk;mta=mx4.tb;d=20220411;t=214936[CET];ipsrc=85.119.84.35;

Here is the reverse zone file ( /var/lib/bind/35-32.84.119.85) for the IP address
$ORIGIN .
$TTL 600 ; 10 minutes
35.84.119.85.in-addr.arpa. IN SOA ns2.keiths-place.co.uk. keith.keiths-place.co.uk. (
2019120307
600
300
1209600
300 )
NS ns1.keiths-place.co.uk.
NS ns2.keiths-place.co.uk.
NS ns3.keiths-place.co.uk.
$ORIGIN 35.84.119.85.in-addr.arpa.
PTR keynesmail.com.
PTR www.keynesmail.com.
PTR mx10.keynesmail.com.
PTR webmail.keynesmail.com.
PTR aakanee.com.
PTR www.aakanee.com.
PTR leightonbuzzard.net.
PTR keiths.space.
PTR www.keiths.space.
PTR splog.keiths.space.
PTR ns1.keiths-place.co.uk.
PTR www.leightonbuzzard.net.
PTR newportpagnell.net.
PTR www.newportpagnell.net.
PTR mail.wingravegolf.co.uk.
PTR webmail.wingravegolf.co.uk.

And the forward zone (keynesmail.com)

$ttl 38400
keynesmail.com. IN SOA ns3.keiths-place.co.uk. keithwilliamsnp.gmail.com. (
2019120313
10800
3600
604800
38400 )
keynesmail.com. IN NS ns3.keiths-place.co.uk.

keynesmail.com. IN NS ns1.keiths-place.co.uk.
keynesmail.com. IN NS ns2.keiths-place.co.uk.

keynesmail.com. IN A 85.119.84.35
www.keynesmail.com. IN A 85.119.84.35
webmail.keynesmail.com. IN A 85.119.84.35

keynesmail.com. IN MX 10 keynesmail.com.
keynesmail.com. IN AAAA 2001:ba8:1f1:f309::2
www.keynesmail.com. IN AAAA 2001:ba8:1f1:f309::2
webmail.keynesmail.com. IN AAAA 2001:ba8:1f1:f309::2
adminmail.keynesmail.com. IN A 85.119.84.35
mx10.keynesmail.com. IN A 85.119.84.35
35.84.119.85.in-addr.arpa. IN PTR mx10.keynesmail.com.
35.84.119.85.in-addr.arpa. IN PTR keynesmail.com.
_dmarc.keynesmail.com. IN TXT "v=DMARC1; p=none; pct=90; adkim=r; aspf=s"

The formatting seems to have gone haywire as I copied and pasted, there.

I am totally stumped, IPv6 works just fine

Keith

On Tue, 12 Apr 2022 at 07:28, John Winters <john@sinodun.org.uk> wrote:

On 12/04/2022 01:12, Andy Smith wrote:
[snip]
> Note that it is not really important that the reverse and forward
> DNS records match anything that is in the email headers, just that
> they match *each other* (reverse DNS resolves to a host name that
> also resolves back to the same IP address).

This used to be the case but I hit a problem the other day of an ISP who
insisted not only that they matched each other but that they also
matched the name given in the HELO part of the SMTP dialogue.

This was a new requirement from that ISP which caused email to bounce.
A nuisance when you have several logical mail servers behind a single
IPv4 address.

So much easier with ISPs who are up to date and use IPv6.

John

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