SpamAssassin (spamd) service is down: no 'mirrors.updates.spamassassin.org' record found, channel failed

Symptoms

After installing or updating cPanel, SpamAssassin is unable to start. Running the sa-update script with the -D and -vvv options fails with messages similar to the following.

Apr  3 12:52:51.069 [887003] dbg: dns: query failed: 6.4.3.updates.spamassassin.org = REFUSED
DNS TXT query 6.4.3.updates.spamassassin.org failed: REFUSED
Apr  3 12:52:51.070 [887003] dbg: dns: query failed: mirrors.updates.spamassassin.org = REFUSED
DNS TXT query mirrors.updates.spamassassin.org failed: REFUSED
channel 'updates.spamassassin.org': no 'mirrors.updates.spamassassin.org' record found, channel failed
Apr  3 12:52:51.070 [887003] dbg: diag: updates complete, exiting with code 4
Update failed, exiting with code 4

Description 

SpamAssassin probes for DNS TXT records when attempting to install or stage the rule updates. If the TXT record can't be received, this kind of failure will occur, which causes the service to fail during restarts. SpamAssassin can't start without rules being installed.

Updating /etc/reolv.conf to use resolvers that return TXT records and restarting SpamAssassin will correct this issue.

Workaround

Please note that you should contact the server's network provider to determine what resolvers should be used.

1. Access the server's command line as the 'root' user via SSH or "Terminal" in WHM.
2. Open /etc/resolv.conf in your preferred text editor.
3. Replace the existing resolvers with the correct resolvers.
4. Save the changes and exit the text editor.
5. Update the SpamAssassin rules.

   /usr/local/cpanel/3rdparty/perl/$perlversion/bin/sa-update -D

   Please note that "$perlversion" must be replaced with most recent version of Perl in the /usr/local/cpanel/3rdparty/perl folder.
6. Restart SpamAssassin.

   /usr/local/cpanel/scripts/restartsrv_spamd