Use unbound for rspamd DNS resolving

To not run into rate-limits when resolving DNS records from rspamd, use
our own local recursive resolver.

playbooks/mail.archlinux.org.yml

@@ -13,7 +13,7 @@
     - { role: postfix, postfix_server: true, postfix_smtpd_public: true, tags: ['mail'] }
     - { role: dovecot }
     - { role: rspamd, tags: ["mail"] }
-    - { role: unbound, tags: ["mail"] }
+    - { role: unbound, unbound_port: 5353, tags: ["mail"] }
     - { role: postfwd, tags: ['mail'] }
     - { role: archusers }
     - { role: fail2ban }

roles/rspamd/files/local.d/options.inc

+dns {
+    nameserver = ["127.0.0.1:5353"];
+}
+