Raise domain name length to RFC1035 maximum (#2147)

RFC1035 Section 2.3.4. specifies a maximum domain name length of 255
octets in protocol. As each label is prefixed by its length and the
domain-root (.) has a length of 0 we have a maximum of 253 octets. For
modoboa to support all these domains in its DB scheme we need to raise
the maximum domain name length to 253 as well.

modoboa/admin/migrations/0019_auto_20210130_2226.py

@@ -0,0 +1,18 @@
+# Generated by Django 2.2.17 on 2021-01-30 22:26
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('admin', '0018_update_disabled_accounts_aliases'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='domain',
+            name='name',
+            field=models.CharField(help_text='The domain name', max_length=253, unique=True, verbose_name='name'),
+        ),
+    ]

modoboa/admin/models/domain.py

@@ -23,7 +23,7 @@ from . import mixins
 class Domain(mixins.MessageLimitMixin, AdminObject):
     """Mail domain."""
 
-    name = models.CharField(ugettext_lazy("name"), max_length=100, unique=True,
+    name = models.CharField(ugettext_lazy("name"), max_length=253, unique=True,
                             help_text=ugettext_lazy("The domain name"))
     quota = models.PositiveIntegerField(
         default=0,