diff --git a/roles/dnsbl_exporter/templates/etc/prometheus/dnsbl-exporter/targets.ini.j2 b/roles/dnsbl_exporter/templates/etc/prometheus/dnsbl-exporter/targets.ini.j2
index aa50194..e011618 100644
--- a/roles/dnsbl_exporter/templates/etc/prometheus/dnsbl-exporter/targets.ini.j2
+++ b/roles/dnsbl_exporter/templates/etc/prometheus/dnsbl-exporter/targets.ini.j2
@@ -2,7 +2,7 @@
 
 [targets]
 {% for host in hostvars.keys() %}
-{% if hostvars[host].monitor_dnsbl | default(false) %}
+{% if hostvars[host].monitor_dnsbl | default('false') | bool %}
 server={{ host }}
 {% endif %}
 {% endfor %}
\ No newline at end of file
diff --git a/roles/prometheus/templates/blackbox.yml b/roles/prometheus/templates/blackbox.yml
index 6a2d77f..dbfc0da 100644
--- a/roles/prometheus/templates/blackbox.yml
+++ b/roles/prometheus/templates/blackbox.yml
@@ -117,6 +117,20 @@ modules:
         - expect: "^250 .*$"
         - send: "QUIT"
 
+  smtp_submission:
+    prober: tcp
+    timeout: 2s
+    tcp:
+      {% if blackbox_prefer_ipv4 -%}
+      preferred_ip_protocol: ip4
+      {% endif -%}
+      query_response:
+        - starttls: true
+        - expect: "^220 .*SMTP .*$"
+        - send: "HELO {{ blackbox_smtp_name }}"
+        - expect: "^250 .*$"
+        - send: "QUIT"
+
   smtps:
     prober: tcp
     timeout: 2s