Can't Receive Mail after BIND Upgrade

[Shon Stephens]

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Upgraded to BIND 9.1.1. Now one of our ISP partners can't sendmail to
our sendmail server. They recieve a "nameserver timeout" error on
their sendmail server. Our sendmail configuration has not changed,
neither have the zone files. Only the version of BIND. Here is my
named.conf file. Its been cleaned up for security. Any ideas? I don't
know yet what type or version of nameserver the partner is using.

options {
        directory "/var/named"; 
        // named-xfer OBSOLETE IN BIND9
        dump-file "/var/named/dump.db";
        // memstatistics-file NOT YET IMPLEMENTED IN BIND9
        pid-file "/var/named/named.pid";
        statistics-file "/var/named/named.stats";
        auth-nxdomain yes;
        recursion yes;
        zone-statistics yes;
        additional-from-auth yes;
        additional-from-cache yes;
        allow-notify { none; };
        allow-query { any; };
        allow-recursion { any; };
        blackhole { none; };
        max-transfer-time-in 30;
        max-transfer-idle-in 30;
        transfer-format many-answers;
        transfers-in 10;
        cleaning-interval 30;
        // statistics-interval NOT YET IMPLEMENTED IN BIND9.
        max-ncache-ttl 86400;
        max-cache-ttl 86400;
};
zone "." {
        type hint;
        file "named.root";
};
zone "0.0.127.in-addr.arpa" {
        type master;
        allow-update { none; };
        file "127.0.0.db";
};
zone "1.1.10.in-addr.arpa" {
        type master;
        allow-update { none; };
        file "10.1.1.db";
};

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