diff --git a/server/utils/email.py b/server/utils/email.py
index a88bc2b..5b3353b 100644
--- a/server/utils/email.py
+++ b/server/utils/email.py
@@ -18,11 +18,17 @@ class Domains:
     aliases: tuple[str, ...]
 
 
+def subdomain_of(domain: str, parent: str) -> bool:
+    """Check if the `domain` is a subdomain of `parent`."""
+    return domain == parent or domain.endswith(f".{parent}")
+
+
 def normalize_email(
     address: str,
     tag: str | None = "+",
     dots: bool = True,
     domains: Domains | None = None,
+    allow_subdomains: bool = True,
 ) -> str:
     """
     Normalize an email address.
@@ -32,6 +38,7 @@ def normalize_email(
     - If provided, remove the `tag` character (+) and everything after it
     - If requested, remove dots (.) from the address
     - If provided, replace the domain with the primary domain if it is an alias
+    - If requested, remove subdomains from the domain
 
     You must have previously validated the email address.
 
@@ -45,8 +52,13 @@ def normalize_email(
         local = local.split(tag, maxsplit=1)[0]
     if dots:
         local = local.replace(".", "")
-    if domains and domain in domains.aliases:
-        domain = domains.primary
+    if domains:
+        if allow_subdomains and any(
+            subdomain_of(domain, d) for d in [domains.primary, *domains.aliases]
+        ):
+            domain = domains.primary
+        elif not allow_subdomains and domain in domains.aliases:
+            domain = domains.primary
     # FORCE ascii for now (yes, this is absurd).
     local = local.encode("ascii", "ignore").decode("ascii")
     domain = domain.encode("ascii", "ignore").decode("ascii")
diff --git a/server/utils/test_email.py b/server/utils/test_email.py
index d7dbe6e..6187264 100644
--- a/server/utils/test_email.py
+++ b/server/utils/test_email.py
@@ -77,3 +77,43 @@ def test_force_ascii(self):
         expected = "tst@xample.com"
         result = e.normalize_email(email)
         self.assertEqual(result, expected)
+
+    def test_allow_subdomains(self):
+        """Test an email address with a subdomain."""
+        email = "test@subdomain.example.com"
+        expected = "test@example.com"
+        domains = e.Domains("example.com", ())
+        result = e.normalize_email(email, domains=domains, allow_subdomains=True)
+        self.assertEqual(result, expected)
+
+    def test_allow_submdomains_invalid(self):
+        """Test an email address with a non-subdomain."""
+        email = "test@subdomainexample.com"
+        expected = "test@subdomainexample.com"
+        domains = e.Domains("example.com", ())
+        result = e.normalize_email(email, domains=domains, allow_subdomains=True)
+        self.assertEqual(result, expected)
+
+    def test_allow_subdomains_aliases(self):
+        """Test an email address with domain aliases and subdomains."""
+        email = "test@party.example.edu"
+        expected = "test@example.com"
+        domains = e.Domains("example.com", ("example.edu",))
+        result = e.normalize_email(email, domains=domains, allow_subdomains=True)
+        self.assertEqual(result, expected)
+
+    def test_disallow_subdomains(self):
+        """Test an email address with a subdomain."""
+        email = "test@subdomain.example.com"
+        expected = "test@subdomain.example.com"
+        domains = e.Domains("example.com", ())
+        result = e.normalize_email(email, domains=domains, allow_subdomains=False)
+        self.assertEqual(result, expected)
+
+    def test_disallow_subdomains_aliases(self):
+        """Test an email address with domain aliases and subdomains."""
+        email = "test@party.example.edu"
+        expected = "test@party.example.edu"
+        domains = e.Domains("example.com", ("example.edu",))
+        result = e.normalize_email(email, domains=domains, allow_subdomains=False)
+        self.assertEqual(result, expected)
diff --git a/server/vb/migrations/0013_add_subdomains_flag.py b/server/vb/migrations/0013_add_subdomains_flag.py
new file mode 100644
index 0000000..957097e
--- /dev/null
+++ b/server/vb/migrations/0013_add_subdomains_flag.py
@@ -0,0 +1,18 @@
+# Generated by Django 5.0.3 on 2024-05-17 17:20
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('vb', '0012_add_percent_voted'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='school',
+            name='allow_subdomains',
+            field=models.BooleanField(default=True, help_text='Whether to allow arbitrary subdomains in school emails.'),
+        ),
+    ]
diff --git a/server/vb/models.py b/server/vb/models.py
index 2e871ae..81577f5 100644
--- a/server/vb/models.py
+++ b/server/vb/models.py
@@ -51,6 +51,10 @@ class School(models.Model):
         default=True,
         help_text="Whether to remove dots from the local part of school emails.",
     )  # noqa
+    allow_subdomains = models.BooleanField(
+        default=True,
+        help_text="Whether to allow arbitrary subdomains in school emails.",
+    )
 
     logo: "Logo"
     contests: "ContestManager"
@@ -64,6 +68,7 @@ def normalize_email(self, address: str) -> str:
             tag=self.mail_tag if self.mail_tag else None,
             dots=self.mail_dots,
             domains=domains,
+            allow_subdomains=self.allow_subdomains,
         )
 
     def hash_email(self, address: str) -> str: