refactor MailProvider model and enhance email validation in admin form

api/migrations/0002_alter_mailprovider_host.py

@@ -0,0 +1,18 @@
+# Generated by Django 5.2.1 on 2025-05-27 21:48
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('api', '0001_initial'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='mailprovider',
+            name='host',
+            field=models.CharField(max_length=255),
+        ),
+    ]