Simply changed:
127.0.0.1 localhost localhost.localdomain
127.0.0.1 foo.bar
To this
127.0.0.1 localhost localhost.localdomain foo.bar
Sendmail looks for a fully qualified domain (FQDN) name and will use the localhost.localdomain in the single line version.
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
Best Answer
Reference