sendmail: SMTP host name lookup failure

Question

I haven't made any changes to sendmail and now it's failing to send any email out due to this error (I use my ISPs SMTP server):

Jan 28 10:34:36 zenorebirth sm-mta[3225]: p0S9htol031342: to=test@gmail.com, delay=05:50:00, xdelay=00:00:00, mailer=relay, pri=17278301, relay=smtp-server.nycap.rr.com, dsn=4.0.0, stat=Deferred: Name server: smtp-server.nycap.rr.com: host name lookup failure

I can telnet into smtp-server.nycap.rr.com and send mail from the Linux machine just fine. Debug info:

# sendmail -v -d8.20 -qIp0SFnrG2009232

Running /var/spool/mqueue/p0SFnrG2009232 (sequence 1 of 1)
dns_getcanonname(zeno.biyg.org, trymx=1)
dns_getcanonname: trying zeno.biyg.org. (A)
        YES
dns_getcanonname: zeno.biyg.org
dns_getcanonname(biyg.net, trymx=1)
dns_getcanonname: trying biyg.net. (A)
        YES
dns_getcanonname: biyg.net
getmxrr(smtp-server.nycap.rr.com, droplocalhost=1)
getmxrr: res_search(smtp-server.nycap.rr.com) failed (errno=110, h_errno=2)
<zeno@biyg.net>... Deferred: Name server: smtp-server.nycap.rr.com: host name lookup failure

Also:

# echo "/map host smtp-server.nycap.rr.com" | sendmail -d8.20 -bt
ADDRESS TEST MODE (ruleset 3 NOT automatically invoked)
Enter <ruleset> <address>
> map_lookup: host (smtp-server.nycap.rr.com) dns_getcanonname(smtp-server.nycap.rr.com, trymx=1)
dns_getcanonname: trying smtp-server.nycap.rr.com. (A)
        YES
dns_getcanonname: smtp-server.nycap.rr.com
returns smtp-server.nycap.rr.com. (0)
>

sendmail.cf: http://pastebin.com/uXxZCZwS

Answer 1

I'm going out on a bit of a limb here, but I think the problem is your remote host ...

getmxrr(smtp-server.nycap.rr.com, droplocalhost=1)
getmxrr: res_search(smtp-server.nycap.rr.com) failed (errno=110, h_errno=2)
<zeno@biyg.net>... Deferred: Name server: smtp-server.nycap.rr.com: host name lookup failure

It looks like res_search is the culprit here and what it's searching for (smtp-server.nycap.rr.com) is producing the error. According to netdb.h (I think) that error is either non-authoritative host or SRVFAIL.

Checking dns, it does look like something's wrong with that host (please forgive the use of nslookup) :

Non-authoritative answer:
Name:   smtp-server.nycap.rr.com
Address: 75.180.132.33

nslookup
> set q=ptr
> 75.180.132.33

Non-authoritative answer:
33.132.180.75.in-addr.arpa      name = cdptpa-omtalb.mail.rr.com.

I want to say it looks like a forward/reverse mismatch, but I could be wrong. It could just be one bad entry in their mailcluster. I'm thinking the reason that it works in the debug mode is that ruleset 3 is skipped and part of that ruleset is doing reverse lookups on the destination mailserver.

You might be able to solve this with a mailertable, that would go a ways towards fingering DNS info as the culprit. Take a look at this -- Solving hostname lookup failures in sendmail