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Sendmail Server Spamhaus DNSBL rejecting all incoming email
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Your sendmail.mc (freebsd.mc) is properly configured to use dnsbl and suddenly all incoming email is rejected.

FEATURE(`dnsbl', `bl.spamcop.net', `"554 Rejected: Unsolicited e-mail from " $`'&{client_addr} " has been refused. DNSBL list: SpamCop (bl.spamcop.net)."', `t')dnl
FEATURE(`dnsbl', `zen.spamhaus.org', `"554 Rejected: Unsolicited e-mail from " $`'&{client_addr} " has been refused. DNSBL list: Spamhaus (zen.spamhaus.org)."', `t')dnl


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Cause
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https://www.spamhaus.org/resource-hub/email-security/service-update-spamhaus-dnsbl-users-who-query-via-cloudflare-dns-need-to-make-changes-to-email-set-up/

https://www.spamhaus.com/resource-center/if-you-query-spamhaus-projects-dnsbls-via-cloudflares-dns-move-to-the-free-data-query-service/


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Easy Fix /etc/resolv.conf
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Do not use Cloudfair DNS nameservers on your sendmail server.

1.1.1.1         cloudfair
1.0.0.1         cloudfair

Just use any other DNS nameserver or set up your own bind server.

9.9.9.9         quad9
149.112.112.112 quad9
208.67.222.222  opendns
208.67.220.220  opendns
84.200.68.80    dnswatch
84.200.70.40    dnswatch
94.140.14.14    adguard
94.140.15.15    adguard
185.228.168.9   cleanbrowsing
185.228.169.9   cleanbrowsing
76.76.2.0       controld
76.76.10.0      controld
8.8.8.8         google
8.8.4.4         google


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