update the custom domain dns issue email template

cron.py

@@ -720,11 +720,6 @@ def check_custom_domain():
                         custom_domain=custom_domain,
                         domain_dns_url=domain_dns_url,
                     ),
-                    render(
-                        "transactional/custom-domain-dns-issue.html",
-                        custom_domain=custom_domain,
-                        domain_dns_url=domain_dns_url,
-                    ),
                     max_nb_alert=1,
                     nb_day=30,
                 )

templates/emails/transactional/custom-domain-dns-issue.html

@@ -1,23 +0,0 @@
-{% extends "base.html" %}
-
-{% block content %}
-  {% call text() %}
-    <h1>
-      <b>{{ custom_domain.domain }}</b> does not have the DNS set up correctly
-    </h1>
-  {% endcall %}
-
-  {% call text() %}
-    Please make sure to set up your domain following the instructions on your domain DNS page at
-    <a href="{{ domain_dns_url }}">{{ custom_domain.domain }} DNS</a>.
-  {% endcall %}
-
-  {% call text() %}
-    Feel free reply to this email if you have any question. <br>
-    Best, <br>
-    SimpleLogin team.
-  {% endcall %}
-
-{% endblock %}
-
-

templates/emails/transactional/custom-domain-dns-issue.txt.jinja2

@@ -1,7 +1,9 @@
-We have detected that your domain {{ custom_domain.domain }} does not have the DNS set up correctly.
+We have detected that your domain {{ custom_domain.domain }} doesn't have the DNS MX records correctly set up.
 
-Please make sure to set up your domain following the instructions on your domain DNS page at:
-{{ domain_dns_url }}
+Please re-run the MX check on {{ domain_dns_url }} and update them if needed.
+
+Without the MX records correctly set up, emails sent to the {{ custom_domain.domain }}'s aliases
+  aren't properly and reliably handled.
 
 Feel free reply to this email if you have any question.