Send branded HTML emails and harden SMTP2GO webhooks.

Fix campaign stuck on sending under async queue, and stop UUID ValidationError when SMTP2GO tests send "Headers Unavailable".

site/messaging/providers/email/smtp2go.py

@@ -2,9 +2,11 @@
 
 from django.conf import settings
 from django.core.mail import EmailMultiAlternatives
+from django.template.loader import get_template
 
 from contacts.models import Channel
 from messaging.services import one_click_unsubscribe_url, preferences_url
+from public.email_branding import email_brand_context, plain_text_to_email_html
 
 # Reported back on SMTP2GO webhooks when this header is selected in webhook settings.
 MONICA_MESSAGE_HEADER = "X-Monica-Message-Id"
@@ -28,15 +30,20 @@ def send_email(message) -> str:
     one_click_path = one_click_unsubscribe_url(str(contact.pk), Channel.EMAIL)
     prefs_url = f"{site}{prefs_path}" if site else prefs_path
     one_click_url = f"{site}{one_click_path}" if site else one_click_path
-    body_with_unsub = (
-        f"{body}\n\n---\n"
-        f"Manage preferences: {prefs_url}\n"
-        f"Unsubscribe from email: {one_click_url}"
+
+    ctx = email_brand_context(
+        title=subject,
+        content=body,
+        content_html=plain_text_to_email_html(body),
+        prefs_url=prefs_url,
+        one_click_url=one_click_url,
     )
+    text_content = get_template("emails/marketing_email.txt").render(ctx)
+    html_content = get_template("emails/marketing_email.html").render(ctx)
 
     email = EmailMultiAlternatives(
         subject=subject,
-        body=body_with_unsub,
+        body=text_content,
         from_email=settings.DEFAULT_FROM_EMAIL,
         to=[contact.email],
         headers={
@@ -45,6 +52,7 @@ def send_email(message) -> str:
             MONICA_MESSAGE_HEADER: str(message.pk),
         },
     )
+    email.attach_alternative(html_content, "text/html")
     email.send(fail_silently=False)
     # Placeholder until SMTP2GO webhook supplies the real email_id.
     return f"smtp-{message.pk}"