diff --git a/server/mergin/auth/forms.py b/server/mergin/auth/forms.py
index b45638eb..f7403bb8 100644
--- a/server/mergin/auth/forms.py
+++ b/server/mergin/auth/forms.py
@@ -1,6 +1,7 @@
 # Copyright (C) Lutra Consulting Limited
 #
 # SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-MerginMaps-Commercial
+
 import re
 import safe
 from flask_wtf import FlaskForm
@@ -48,18 +49,22 @@ class ExtendedEmail(Email):
     1. spaces,
     2. special characters ,:;()<>[]\"
     3, multiple @ symbols,
-    4, leading, trailing, or consecutive dots in the local part
-    5, invalid domain part - missing top level domain (user@example), consecutive dots
-    Custom check for additional invalid characters disallows |'— because they make our email sending service to fail
+    4, leading, trailing, or consecutive dots in the local part,
+    5, invalid domain part - missing top level domain (user@example), consecutive dots,
+    The extended validation checks email addresses using the regex provided by Brevo,
+    so that we stay consistent with their validation rules and avoid API failures.
     """
 
     def __call__(self, form, field):
         super().__call__(form, field)
 
-        if re.search(r"[|'—]", field.data):
-            raise ValidationError(
-                f"Email address '{field.data}' contains an invalid character."
-            )
+        email = field.data.strip()
+
+        pattern = r"^[\x60#&*\/=?^{!}~'+\w-]+(\.[\x60#&*\/=?^{!}~'+\w-]+)*\.?@([_a-zA-Z0-9-]+(\.[_a-zA-Z0-9-]+)*\.)[a-zA-Z0-9-]*[a-zA-Z0-9]{2,}$"
+        email_regexp = re.compile(pattern, re.IGNORECASE)
+
+        if not email_regexp.match(email):
+            raise ValidationError(f"Email address '{email}' is invalid.")
 
 
 class PasswordValidator:
diff --git a/server/mergin/tests/test_auth.py b/server/mergin/tests/test_auth.py
index d53b01bc..69ba37c6 100644
--- a/server/mergin/tests/test_auth.py
+++ b/server/mergin/tests/test_auth.py
@@ -125,9 +125,14 @@ def test_logout(client):
         400,
     ),  # tests with upper case, but email already exists
     (" mergin@mergin.com  ", "#pwd123", 400),  # invalid password
-    ("verylonglonglonglonglonglonglongemail@example.com", "#pwd1234", 201),
+    (
+        "verylonglonglonglonglonglonglongemail@lutra-consulting.co.uk",
+        "#pwd1234",
+        201,
+    ),  # long local part, second-level domain, dash in domain
     ("us.er@mergin.com", "#pwd1234", 201),  # dot is allowed
     ("us er@mergin.com", "#pwd1234", 400),  # space is disallowed
+    ("test@gmaiñ.com", "#pwd1234", 400),  # non-ASCII character in the domain
 ]
 
 
@@ -936,15 +941,16 @@ def test_server_usage(client):
     ("日人日本人", True),  # non-ascii character
     ("usér", True),  # non-ascii character
     ("user\\", False),  # disallowed character
-    ("user\260", True),  # non-ascii character (°)
+    ("user\260", False),  # not letter character (°)
     ("user|", False),  # vertical bar
     ("us er", False),  # space in the middle
     ("us,er", False),  # comma
     ("us—er", False),  # dash
-    ("us'er", False),  # apostrophe
+    ("us´er", False),  # acute accent
     (" user", True),  # starting with space (will be stripped)
     ("us.er", True),  # dot in the middle
     (".user", False),  # starting with dot
+    ("us-er", True),  # hyphen
 ]