On 17/06/2026 5:55 am, Patrick Ben Koetter via Postfix-users wrote:
* Al via Postfix-users <[email protected]>:
I have taken a look at my logs:
This is the error:
Jun 9 12:03:41 sequoia postfix/smtpd[52759]: NOQUEUE: reject: RCPT
from
unknown[45.90.5.195]: 554 5.7.1 Client host rejected: cannot find your
reverse hostname, [45.90.5.195];
from=<[email protected]>
to=<[email protected]> proto=ESMTP helo=<list.sys4.de>
However, most of the of the time it lets, it through:
0.43, dsn=2.6.0, status=sent (250 2.6.0 <[email protected]> Message
accepted
for delivery)
Jun 14 06:35:36 sequoia postfix/qmgr[83260]: 4DC2D1F5A07: removed
I added:
[email protected] OK
list.sys4.de has valid PTRs for it's A and AAAA record:
$ dig +short -x 2a03:4000:20:189::195
list.sys4.de.
$ dig -x 45.90.5.195
; <<>> DiG 9.10.6 <<>> -x 45.90.5.195
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 38526
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;195.5.90.45.in-addr.arpa. IN PTR
;; ANSWER SECTION:
195.5.90.45.in-addr.arpa. 43200 IN PTR list.sys4.de.
;; Query time: 54 msec
;; SERVER: 192.168.178.1#53(192.168.178.1)
;; WHEN: Wed Jun 17 11:44:26 CEST 2026
;; MSG SIZE rcvd: 79
The TTL of 43200 is high, so your platform should be able to keep this
cached
for a long time.
It seems (speculation!) the problem is somewhere in your DNS stack, but
we
don't know yet. As Wietse's put it many years ago on the Postfix-Users
list:
"Measure! Don't speculate!".
This is true!
As suggested by other start by looking at your log. If the message
persists
claiming Postfix can't find the reverse PTR and I - the guy running the
DNS
stack for list.sys4.de - have just proven it exists, then the question
is: Why
wouldn't Postfix know then? Between the sys4 nameservers and your
Postfix
there's your DNS stack. I would assume to find the error there.
I would agree. Reverse DNS exists, but I am still looking at why it is
not seeing reverse DNS once in a while.
- Are you running a chrooted Postfix and it can't query the right DNS
resolvers?
Not running a chrooted Postfix.
- What do your DNS resolvers tell if you ask them on command line about
list.sys4.de PTRs?
$ dig +short -x 2a03:4000:20:189::195
$ dig +short -x 45.90.5.195
#dig +short -x 2a03:4000:20:189::195
#dig +short -x 45.90.5.195
list.sys4.de.
The IPV6 returns nothing, so I would think that is the problem, but the
error is with an IPv4 address.
I have not been able to get an IPv6 address from my ISP.
Kind Regards,
Al
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