refactor MailProvider model and enhance email validation in admin form

api/admin.py

@@ -1,4 +1,6 @@
+import logging
 import smtplib
+import socket
 
 from django.contrib import admin
 from django import forms
@@ -6,6 +8,8 @@ from django.core.exceptions import ValidationError
 
 from api.models import MailProvider
 
+_logger = logging.getLogger(__name__)
+
 class MailProviderForm(forms.ModelForm):
     host_password = forms.CharField(widget=forms.PasswordInput(render_value=True))
 
@@ -21,11 +25,26 @@ class MailProviderForm(forms.ModelForm):
         password = cleaned_data.get("host_password")
         use_tls = cleaned_data.get("use_tls")
 
+        if host:
+            try:
+                socket.gethostbyname(host)
+            except socket.gaierror:
+                raise ValidationError(
+                    "Invalid mail server hostname. Could not resolve host."
+                )
+
         if host and port and user and password:
             try:
-                connection = smtplib.SMTP(host, port, timeout=10)
-                if use_tls:
-                    connection.starttls()
+                if port == 465:
+                    connection = smtplib.SMTP_SSL(host, port, timeout=10)
+                else:
+                    connection = smtplib.SMTP(host, port, timeout=10)
+                    if use_tls and port == 465:
+                        raise ValidationError(
+                            "Port 465 should not be used with STARTTLS. Use SMTP_SSL instead or change to port 587."
+                        )
+                    if use_tls:
+                        connection.starttls()
                 connection.login(user, password)
                 connection.quit()
             except Exception as e: