From Newsgroup: comp.mail.sendmail

Hallo!

I am using sendmail 8.18.1 on Debian 13.
systemd-resolve is running as a local stub resolver and working.


u@pi-dach:~$ dig -x 95.216.221.164 @127.0.0.53 +short smtp.eternal-september.org.
u@pi-dach:~$ dig a smtp.eternal-september.org. +short
95.216.221.164
u@pi-dach:~$

u@pi-dach:~$ getent hosts 95.216.221.164
95.216.221.164 smtp.eternal-september.org
u@pi-dach:~$



That happens for multiple servers, so it is not an issue of this
specific sending server.

It does work for IPv6 sending servers, but not for IPv4.

How can I further diagnose this?

I've tried -bt and saw the proper queries in the tcpdump.
Although, it does not display the results in the -bt mode (maybe I use
it wrong).
--
kind regards
Marco

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From Newsgroup: comp.mail.sendmail

Marco Moock wrote:

That happens for multiple servers, so it is not an issue of this

What is "that"?

How can I further diagnose this?

What is the problem you have with sendmail?

I've tried -bt and saw the proper queries in the tcpdump.
Although, it does not display the results in the -bt mode (maybe I use
it wrong).

You don't show what you are doing, so how to tell what might be wrong?
--- Synchronet 3.21f-Linux NewsLink 1.2

From Newsgroup: comp.mail.sendmail

On 06.04.2026 12:29 Uhr Claus A|fmann wrote:

Marco Moock wrote:

That happens for multiple servers, so it is not an issue of this

What is "that"?

Messages are being rejected because sendmail thinks the PTR doesn't
match the hostname, but DNS works properly.

How can I further diagnose this?

What is the problem you have with sendmail?

Fix reverse DNS for 192.55.226.66
Although, the PTR matches the hostname and vice-versa. This happens for multiple servers.

I've tried -bt and saw the proper queries in the tcpdump.
Although, it does not display the results in the -bt mode (maybe I
use it wrong).

You don't show what you are doing, so how to tell what might be wrong?

ADDRESS TEST MODE (ruleset 3 NOT automatically invoked)
Enter <ruleset> <address>

/dnslookup smtp.eternal-september.org

--
kind regards
Marco
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From Newsgroup: comp.mail.sendmail

Marco Moock wrote:

Messages are being rejected because sendmail thinks the PTR doesn't
match the hostname, but DNS works properly.

Maybe DNS works properly, but whatever your "systemd" crap
is doing is most likely broken.

Example;
If /etc/nsswitch.conf uses myhostname for the hosts service and it
is listed after dns, then a temporary dns failure will result in a
permanent error - which obviously is completely bogus and something
systemd introduced based on a poor decision by some developer(s)


Moreover, why (and how) do you reject message based on this?

/dnslookup smtp.eternal-september.org

Why do you only provide part of the debugging?
What is "dnslookup"? (a map but what's the K line in the cf file)?
What is the output of the command?

What is used to show that the IP does not resolve properly?

Please provide a COMPLETE example of the tests which you
used in sendmail so others can try it too.

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From Newsgroup: comp.mail.sendmail

Oops, sorry, I never use dnslookup because it doesn't print anything
-- unless you turn on debugging:

echo '/dnslookup smtp.eternal-september.org' | ./sendmail -C localrelay.cf -bt -d8.64
ADDRESS TEST MODE (ruleset 3 NOT automatically invoked)
Enter <ruleset> <address>

dns_lookup_int(smtp.eternal-september.org, 1, A, 0)

dns_lookup_int(smtp.eternal-september.org, 1, A, 0)=60
parse_dns_reply: ac=1, ad=0
parse_dns_reply: IPv4=95.216.221.164

echo '/dnslookup 164.221.216.95.in-addr.arpa ptr' | ./sendmail -C localrela>->
ADDRESS TEST MODE (ruleset 3 NOT automatically invoked)
Enter <ruleset> <address>

dns_lookup_int(164.221.216.95.in-addr.arpa, 1, PTR, 0)

dns_lookup_int(164.221.216.95.in-addr.arpa, 1, PTR, 0)=85
parse_dns_reply: ac=1, ad=0
parse_dns_reply: type=PTR, host=smtp.eternal-september.org

--- Synchronet 3.21f-Linux NewsLink 1.2

From Newsgroup: comp.mail.sendmail

On 06.04.2026 15:18 Uhr Claus A|fmann wrote:

Marco Moock wrote:

Messages are being rejected because sendmail thinks the PTR doesn't
match the hostname, but DNS works properly.

Maybe DNS works properly, but whatever your "systemd" crap
is doing is most likely broken.

Example;
If /etc/nsswitch.conf uses myhostname for the hosts service and it
is listed after dns, then a temporary dns failure will result in a
permanent error - which obviously is completely bogus and something
systemd introduced based on a poor decision by some developer(s)

hosts: files myhostname resolve [!UNAVAIL=return] dns
That is the default when installing Debian.

Moreover, why (and how) do you reject message based on this?

Certain spammer-controlled systems have improper rdns - normal mail
relays have set PTR records properly.
I used FEATURE(`require_rdns')dnl in the past for that.

/dnslookup smtp.eternal-september.org

Why do you only provide part of the debugging?
What is "dnslookup"? (a map but what's the K line in the cf file)?
What is the output of the command?

u@pi-dach:~$ echo '/dnslookup smtp.eternal-september.org AAAA' | sudo sendmail -bt -d8.64
_res.options = 41012c3, HasWildcardMX = 0
ADDRESS TEST MODE (ruleset 3 NOT automatically invoked)
Enter <ruleset> <address>

dns_lookup_int(smtp.eternal-september.org, 1, AAAA, 0)

dns_lookup_int(smtp.eternal-september.org, 1, AAAA, 0)=83
parse_dns_reply: ac=1, ad=0
dns2he: ad=0

u@pi-dach:~$ echo '/dnslookup smtp.eternal-september.org A' | sudo
sendmail -bt -d8.64

_res.options = 41012c3, HasWildcardMX = 0
ADDRESS TEST MODE (ruleset 3 NOT automatically invoked)
Enter <ruleset> <address>

dns_lookup_int(smtp.eternal-september.org, 1, A, 0)

dns_lookup_int(smtp.eternal-september.org, 1, A, 0)=71
parse_dns_reply: ac=1, ad=0
parse_dns_reply: IPv4=95.216.221.164
dns2he: ad=0

u@pi-dach:~$
u@pi-dach:~$ echo '/dnslookup 164.221.216.95.in-addr.arpa PTR ' | sudo sendmail -bt -d8.64

_res.options = 41012c3, HasWildcardMX = 0
ADDRESS TEST MODE (ruleset 3 NOT automatically invoked)
Enter <ruleset> <address>

dns_lookup_int(164.221.216.95.in-addr.arpa, 1, PTR, 0)

dns_lookup_int(164.221.216.95.in-addr.arpa, 1, PTR, 0)=96
parse_dns_reply: ac=1, ad=0
parse_dns_reply: type=PTR, host=smtp.eternal-september.org
dns2he: ad=0

u@pi-dach:~$
What is used to show that the IP does not resolve properly?

STARTTLS=server, relay=[95.216.221.164]
Normally, the host name is listed there if DNS lookup is working.
--
kind regards
Marco
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From Newsgroup: comp.mail.sendmail

Marco Moock wrote:

dns_lookup_int(smtp.eternal-september.org, 1, A, 0)=71
parse_dns_reply: IPv4=95.216.221.164

dns_lookup_int(164.221.216.95.in-addr.arpa, 1, PTR, 0)=96
parse_dns_reply: type=PTR, host=smtp.eternal-september.org

As expected DNS is working ok.
However, DNS is not used directly for the lookups
thanks to nsswitch.conf.
Hence try
echo '/map resolve [95.216.221.164]' | sendmail -bt
...
map_lookup: resolve ([95.216.221.164]) returns smtp.eternal-september.org<OKR> (0)

If it is something else on your system then you have to figure out
what is broken in nsswitch.conf.

My Alma8 test machine uses
hosts: files dns

Try it with just that to see whether it fixes the problem.
--- Synchronet 3.21f-Linux NewsLink 1.2

From Newsgroup: comp.mail.sendmail

On 07.04.2026 14:55 Uhr Claus A|fmann wrote:

Hence try
echo '/map resolve [95.216.221.164]' | sendmail -bt
...
map_lookup: resolve ([95.216.221.164]) returns smtp.eternal-september.org<OKR> (0)

If it is something else on your system then you have to figure out
what is broken in nsswitch.conf.

$ echo '/map resolve [95.216.221.164]' | sudo sendmail -bt
[sudo] password for u:
ADDRESS TEST MODE (ruleset 3 NOT automatically invoked)
Enter <ruleset> <address>

map_lookup: resolve ([95.216.221.164]) returns smtp.eternal-september.org<OKR> (0)

That looks fine for me.
Is there anything else I can test?
--
kind regards
Marco
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From Newsgroup: comp.mail.sendmail

On 08.04.2026 20:44 Uhr Marco Moock wrote:

On 07.04.2026 14:55 Uhr Claus A|fmann wrote:

Hence try
echo '/map resolve [95.216.221.164]' | sendmail -bt
...
map_lookup: resolve ([95.216.221.164]) returns smtp.eternal-september.org<OKR> (0)

If it is something else on your system then you have to figure out
what is broken in nsswitch.conf.

$ echo '/map resolve [95.216.221.164]' | sudo sendmail -bt
[sudo] password for u:
ADDRESS TEST MODE (ruleset 3 NOT automatically invoked)
Enter <ruleset> <address>

map_lookup: resolve ([95.216.221.164]) returns smtp.eternal-september.org<OKR> (0)

That looks fine for me.

Is there anything else I can test?

I've tested to use
hosts: files dns
same result.
--
kind regards
Marco
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From Newsgroup: comp.mail.sendmail

On Wed, 08 Apr 2026 20:46:04 +0200, Marco Moock wrote:

On 08.04.2026 20:44 Uhr Marco Moock wrote:

On 07.04.2026 14:55 Uhr Claus A|fmann wrote:

Hence try
echo '/map resolve [95.216.221.164]' | sendmail -bt
...
map_lookup: resolve ([95.216.221.164]) returns
smtp.eternal-september.org<OKR> (0)

If it is something else on your system then you have to figure out
what is broken in nsswitch.conf.

$ echo '/map resolve [95.216.221.164]' | sudo sendmail -bt
[sudo] password for u:
ADDRESS TEST MODE (ruleset 3 NOT automatically invoked)
Enter <ruleset> <address>

map_lookup: resolve ([95.216.221.164]) returns
smtp.eternal-september.org<OKR> (0)

That looks fine for me.

Is there anything else I can test?

I've tested to use
hosts: files dns
same result.

Just on the off chance that "files" is causing a problem,
is either eternal-september.org or 95.216.221.164 in your
/etc/hosts
or
/etc/networks
files?
--
Lew Pitcher
"In Skills We Trust"
Not LLM output - I'm just like this.
--- Synchronet 3.21f-Linux NewsLink 1.2

From Newsgroup: comp.mail.sendmail

Which OS defines does your system use?
sendmail -bt -d0.13 </dev/null


OS Defines: ADDRCONFIG_IS_BROKEN HASFCHOWN HASFCHMOD
HASGETDTABLESIZE HAS_GETHOSTBYNAME2 HASINITGROUPS HASLSTAT
HASNICE HASRANDOM HASRRESVPORT HASSETREGID HASSETREUID
HASSETRLIMIT HASSETSID HASSETVBUF HASURANDOMDEV HASSTRERROR
HASUNAME HASUNSETENV HASWAITPID IDENTPROTO MILTER_NO_NAGLE
NEEDSGETIPNODE SFS_VFS USE_DOUBLE_FORK USE_SIGLONGJMP


Can you compile "the real thing" and use that?
Maybe your OS provider applies some patches to sendmail?

What are the other log lines for a connection from
smtp.eternal-september.org
that include relay=
?

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From Newsgroup: comp.mail.sendmail

On 08.04.2026 21:23 Uhr Lew Pitcher wrote:

Just on the off chance that "files" is causing a problem,
is either eternal-september.org or 95.216.221.164 in your
/etc/hosts
or
/etc/networks
files?

No, as this is not my hostname/IP.
--
kind regards
Marco

Send spam to 1775676234muell@stinkedores.dorfdsl.de

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From Newsgroup: comp.mail.sendmail

Does this happen all the time or does the IP sometimes resolve?

Please post some log entries which shows relay= other than STARTTLS,
e.g., something like this from= entry:

639Hfi1E097507: from=<info@serviciosdecontrol.com>, ..., relay=career.serviciosdecontrol.com [91.237.124.226] (may be forged)

esp. for smtp.eternal-september.org
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From Newsgroup: comp.mail.sendmail

On 09.04.2026 02:42 Uhr Claus A|fmann wrote:

Which OS defines does your system use?
sendmail -bt -d0.13 </dev/null

OS Defines: ADDRCONFIG_IS_BROKEN HASFCHOWN HASFCHMOD
HASGETDTABLESIZE HAS_GETHOSTBYNAME2 HASINITGROUPS
HASLSTAT HASNICE HASRANDOM HASRRESVPORT HASSETREGID HASSETREUID
HASSETRLIMIT HASSETSID HASSETVBUF HASURANDOMDEV
HASSTRERROR HASUNAME HASUNSETENV HASWAITPID IDENTPROTO MILTER_NO_NAGLE
NEEDSGETIPNODE SFS_VFS USE_DOUBLE_FORK USE_SIGLONGJMP

u@pi-dach:~$ sudo sendmail -bt -d0.13 </dev/null
Version 8.18.1
Compiled with: DANE HAVE_SSL_CTX_dane_enable MAX_TLSA_RR=64 DNSMAP
IPV6_FULL LDAPMAP LDAP_NETWORK_TIMEOUT LDAP_REFERRALS
LOG MAP_REGEX MATCHGECOS MAXDAEMONS=64 MILTER MIME7TO8 MIME8TO7
NAMED_BIND NETINET NETINET6 NETUNIX NEWDB=5.3 NIS
NISPLUS PIPELINING SASLv2 SCANF SOCKETMAP STARTTLS TCPWRAPPERS TLS_EC
TLS_VRFY_PER_CTX USERDB USE_LDAP_INIT XDEBUG
OS Defines: ADDRCONFIG_IS_BROKEN HASFCHOWN HASFCHMOD HASFLOCK
HASGETDTABLESIZE HAS_GETHOSTBYNAME2 HASGETUSERSHELL
HASINITGROUPS HASLSTAT HASNICE HASRANDOM HASRRESVPORT
HASSETREGID HASSETREUID HASSETRLIMIT HASSETSID
HASSETVBUF HASURANDOMDEV HASSTRERROR HASUNAME HASUNSETENV HASWAITPID
IDENTPROTO IP_SRCROUTE NEEDSGETIPNODE REQUIRES_DIR_FSYNC
SFS_VFS USE_DOUBLE_FORK USE_SIGLONGJMP USESETEUID
Kernel symbols: /boot/vmlinux
Conf file: /etc/mail/submit.cf (default for MSP)
Conf file: /etc/mail/sendmail.cf (default for MTA)
Pid file: /var/run/sendmail/mta/sendmail.pid (default)
libsm Defines: SM_CONF_LDAP_INITIALIZE SM_CONF_LDAP_MEMFREE
SM_CONF_LONGLONG SM_CONF_MEMCHR SM_CONF_MSG SM_CONF_SEM
SM_CONF_SIGSETJMP SM_CONF_SHM SM_CONF_SSIZE_T
SM_CONF_STDBOOL_H SM_CONF_STDDEF_H SM_CONF_SYS_CDEFS_H SM_CONF_UID_GID
DO_NOT_USE_STRCPY SM_HEAP_CHECK SM_OS=sm_os_linux
SM_VA_STD FFR Defines: _FFR_BADRCPT_SHUTDOWN _FFR_MAIL_MACRO
_FFR_MTA_STS _FFR_NO_PIPE _FFR_QUEUE_SCHED_DBG _FFR_REJECT_NUL_BYTE
_FFR_RESET_MACRO_GLOBALS _FFR_RHS _FFR_SHM_STATUS
_FFR_SKIP_DOMAINS _FFR_TLS_ALTNAMES _FFR_M_ONLY_IPV4
Canonical name: pi-dach.dorfdsl.de
UUCP nodename: pi-dach.dorfdsl.de
a.k.a.: [IPv6:2xxx3]
a.k.a.: [IPv6:fe80]
a.k.a.: [127.0.0.1]
a.k.a.: []
Conf file: /etc/mail/sendmail.cf (selected)
Pid file: /var/run/sendmail/mta/sendmail.pid (selected)
============ SYSTEM IDENTITY (after readcf) ============
(short domain name) $w = pi-dach
(canonical domain name) $j = pi-dach.dorfdsl.de
(subdomain name) $m = dorfdsl.de
(node name) $k = pi-dach.dorfdsl.de ========================================================
ADDRESS TEST MODE (ruleset 3 NOT automatically invoked)
Enter <ruleset> <address>

u@pi-dach:~$
Can you compile "the real thing" and use that?
Maybe your OS provider applies some patches to sendmail?

I used that version before and it worked. I figured out that
hosts: files myhostname dns
is working, but the default in Debian,
files myhostname resolve [!UNAVAIL=return] dns
is not.
Can you please check if that is an issue in sendmail itself or the libc/systemd-resolve stuff?
--
kind regards
Marco
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From Newsgroup: comp.mail.sendmail

On 09.04.2026 13:48 Uhr Claus A|fmann wrote:

Does this happen all the time or does the IP sometimes resolve?

No, depends on the setting in nsswitch.conf. Although, I have no clue
about the libc stuff, so I cannot figure out the exact cause of the
issue.
--
kind regards
Marco
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From Newsgroup: comp.mail.sendmail

Marco Moock wrote:

On 09.04.2026 13:48 Uhr Claus A|fmann wrote:

Does this happen all the time or does the IP sometimes resolve?

No, depends on the setting in nsswitch.conf. Although, I have no clue

Which setting? So you have a "working" version?

about the libc stuff, so I cannot figure out the exact cause of the
issue.

Neither can I because you don't provide the requested info
(e.g., log entries), hence I give up unless you provide
all needed information.
--- Synchronet 3.21f-Linux NewsLink 1.2

From Newsgroup: comp.mail.sendmail

On Thu, 09 Apr 2026 19:36:18 +0200, Marco Moock wrote:

On 08.04.2026 21:23 Uhr Lew Pitcher wrote:

Just on the off chance that "files" is causing a problem,
is either eternal-september.org or 95.216.221.164 in your
/etc/hosts
or
/etc/networks
files?

No, as this is not my hostname/IP.

Yes? So?

/etc/hosts and /etc/networks are not just for naming /your/
local system, they participate in host and domain name
resolution. If you have "files" ahead of "dns", then
the contents of those two files will be used to resolve
host/network names (including /foreign/ host and network names)
ahead of DNS.
--
Lew Pitcher
"In Skills We Trust"
Not LLM output - I'm just like this.
--- Synchronet 3.21f-Linux NewsLink 1.2

From Newsgroup: comp.mail.sendmail

On 09.04.2026 18:23 Uhr Lew Pitcher wrote:

/etc/hosts and /etc/networks are not just for naming /your/
local system, they participate in host and domain name
resolution. If you have "files" ahead of "dns", then
the contents of those two files will be used to resolve
host/network names (including /foreign/ host and network names)
ahead of DNS.

I know that I can use this file to set the hostname <--> IP relation,
but I do not use it in that case. It only includes stuff for localhost.

myhostname of systemd-resolved does the part for the currently set
hostname.
--
kind regards
Marco

Send spam to 1775751815muell@stinkedores.dorfdsl.de

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From Newsgroup: comp.mail.sendmail

On 09.04.2026 14:23 Uhr Claus A|fmann wrote:

Marco Moock wrote:

On 09.04.2026 13:48 Uhr Claus A|a++mann wrote:

Does this happen all the time or does the IP sometimes resolve?

No, depends on the setting in nsswitch.conf. Although, I have no
clue

Which setting? So you have a "working" version?

Message-ID: <10r8pjc$gtao$6@dont-email.me>
hosts: files myhostname dns
is working, but the default in Debian,
files myhostname resolve [!UNAVAIL=return] dns
is not.
Which means that if the resolve library (systemd-resolved) is available,
the result will be returned and dns will not be used.
So either it does not deliver a proper result or sendmail does not use
it properly.

about the libc stuff, so I cannot figure out the exact cause of the
issue.

Neither can I because you don't provide the requested info
(e.g., log entries), hence I give up unless you provide
all needed information.

Apr 09 19:59:43 pi-dach.dorfdsl.de sm-mta[15803]: 6xxxx:
from=<xxxx>, size=267, class=0, nrcpts=1, msgid=<20xxxxxde>,
proto=ESMTP, daemon=MTA, relay=[82.139.252.16] Apr 09 20:00:03 pi-dach.dorfdsl.de sm-mta[15815]: 6xxx: from=<xxx>,
size=267, class=0, nrcpts=1,
msgid=<202xxx>, proto=ESMTP, daemon=MTA,
relay=srv1.dorfdsl.de [82.139.252.16]
The last one is where I changed nsswitch.conf to
hosts: files myhostname dns
--
kind regards
Marco
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From Newsgroup: comp.mail.sendmail

Marco Moock <mm@dorfdsl.de> writes:

is working, but the default in Debian,

files myhostname resolve [!UNAVAIL=return] dns

That's only default if you install libnss-resolve? I believe that's
optional.

In any case, this problem is well-known and easy to solve: https://github.com/systemd/systemd/issues/29069#issuecomment-1781921909

Or you can simply do `apt purge libnss-resolve`.




Bj|+rn
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From Newsgroup: comp.mail.sendmail

Marco Moock wrote:

I used that version before and it worked. I figured out that

hosts: files myhostname dns

is working, but the default in Debian,

[[... is broken ...]]

Can you please check if that is an issue in sendmail itself or the

It's not in sendmail.

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From Newsgroup: comp.mail.sendmail

On 09.04.2026 20:48 Uhr Bj|+rn Mork wrote:

In any case, this problem is well-known and easy to solve: https://github.com/systemd/systemd/issues/29069#issuecomment-1781921909

Thanks for the pointer.
--
kind regards
Marco
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