[GLLUG] sendmail puzzle

Marco van Beek mvanbeek at supporting-role.co.uk
Tue Oct 11 07:33:55 UTC 2022


It might be the difference between a missing entry in a zone file, and a 
missing zone file. Maybe it is the lookup mechanism that fails, rather 
than it checking the IP address itself. It might be another rule set 
that is trying to do a reverse lookup (eg hostname), and it barfs out at 
that point.

Maybe increase the logging verbosity and check the logs again?



On 10/10/2022 22:54, Ken Smith via GLLUG wrote:
> I'm trying to sort out a Rocky 8.5 server that has sendmail installed. 
> (Please don't go on a diversion about how I should tell the owner to 
> dump sendmail and switch to exim or postfix - save that for another 
> thread please. )
> I'm pretty good with sendmail but this problem has me a bit foxed. I'd 
> value some suggestions of where to look as I think I'm not seeing the 
> wood for the trees.
> It will send from addresses in the local network, without auth, 
> because I have "connect:192.168.123   relay" in the access file - that 
> being the local LAN.
> I've tested sasl auth and that is authenticating.
> Using telnet from an IP off their LAN (over a VPN) I can connect using 
> TLS (openssl s_client etc etc) and authenticate (perl -MMIME::Base64 
> etc etc)  it accepts my credentials and then if I try to send a 
> message I get "Relaying denied. IP name lookup failed [my local ip]" 
> The same happens with a test using Thunderbird.
> If I do the same test from the host that sendmail is on, it works fine.
> Also if I do the same test from another host on the same LAN it works 
> fine.
> Somehow its complaining about the source IP in authenticated sessions 
> outside the LAN range.
> In the test from my local LAN (172.16.0.x), over a VPN, the remote dns 
> can't resolve the reverse dns of my LAN. I've done a similar test with 
> another sendmail site and remote auth is working fine.
> Maybe sendmail is doing reverse DNS when it shouldn't be.
> Suggestions most welcome....
> Thanks
> Ken

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