LinuxQuestions.org - Sendmail doesn't resolve domain names

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Sendmail doesn't resolve domain names

This is what happens when fetchmail pulls emails (a line from /var/log/maillog):

Code:

sm-mta[2354]: kAC0K9it002354: ruleset=check_mail, arg1=<mplayer-dev-eng-bounces@mplayerhq.hu>, relay=localhost [127.0.0.1],

 reject=451 4.1.8 Domain of sender address mplayer-dev-eng-bounces@mplayerhq.hu does not resolve

Everything worked fine, until I had to go on a trip. Then this started to happen.

I solved it by adding this to sendmail.cf (actually, added it to sendmail.mc, but sendmailers over there know what I'm talking about):

Code:

FEATURE(`accept_unresolvable_domains')dnl

My laptop is firewalled, so I won't get any spam or such. So this solved my problem.

But, does anybody know just what have happened here? I can dig those mxs, why sendmail can't? Just so you know, I've done my share of RTFMing, but I haven't find definite answer to what's going on.

It took me 3 attempts to resolve their domain just now. Maybe their DNS info needs to be retrieved via a slow link - I was getting the error DNS request timed out.

Does this happen for other domains as well?

Well, it happened for all domains (even gmail.com), until I turned off domain checking. That's bugging me: I can dig mx for every domain, but sendmail can't.

Do you do your DNS lookups directly from the root DNS servers? The recommendation at http://www.sendmail.org/tips/private-dns/ is to set up your own DNS server as a forwarding server (pointing to your ISP's DNS) and change your clients' DNS settings to use your DNS.

Sendmail should use the DNS servers set up in the local /etc/resolv.conf file for its lookups.

Yup, I use forwarding DNS server. And /etc/resolv.conf is:

nameserver 192.168.1.1

But, I've tried putting OpenDNS' servers in my resolv.conf, and still I would get the same error messages.