diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 2d3117330..2722e8ed7 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -49,7 +49,13 @@ jobs:
       - name: Install tox
         run: pip install tox
       - name: Write liberapay environment file for tests
-        run: echo 'DATABASE_URL="port=5432 dbname=liberapay_tests"' >tests/local.env
+        run: |
+          cat >tests/local.env <<EOF
+          DATABASE_URL="port=5432 dbname=liberapay_tests"
+          # As of March 2025, GitHub Actions runners still don't have IPv6,
+          # so we override the default IPv6-only test email address here.
+          TEST_EMAIL_ADDRESS=test@changaco.net
+          EOF
       - name: Run the tests
         run: tox
       - name: Upload coverage reports to Codecov
diff --git a/defaults.env b/defaults.env
index de2caec09..dd3977b5f 100644
--- a/defaults.env
+++ b/defaults.env
@@ -52,3 +52,4 @@ INSTANCE_TYPE=development
 SECRET_FERNET_KEYS="2019-01-19 This_is_a_fake_key_of_32_bytes_in_Base64URL="
 
 HOSTNAME=
+TEST_EMAIL_ADDRESS=test@ipv6.changaco.net
diff --git a/liberapay/utils/emails.py b/liberapay/utils/emails.py
index 6442fff21..12ceeac68 100644
--- a/liberapay/utils/emails.py
+++ b/liberapay/utils/emails.py
@@ -167,7 +167,7 @@ def check_email_address(email: NormalizedEmailAddress) -> None:
                 if port_25_is_open is None:
                     try:
                         test_email_address(normalize_email_address(
-                            'support@liberapay.com'
+                            website.env.test_email_address
                         ))
                     except BrokenEmailDomain:
                         port_25_is_open = False
diff --git a/liberapay/website.py b/liberapay/website.py
index 9b16b44b8..acd9a425f 100644
--- a/liberapay/website.py
+++ b/liberapay/website.py
@@ -89,6 +89,7 @@ env = Environment(
     COMPRESS_ASSETS=is_yesish,
     CSP_EXTRA=str,
     HOSTNAME=str,
+    TEST_EMAIL_ADDRESS=str,
     SENTRY_DEBUG=is_yesish,
     SENTRY_DSN=str,
     SENTRY_RERAISE=is_yesish,
diff --git a/tests/py/test_email.py b/tests/py/test_email.py
index 370e42f86..faa7ec585 100644
--- a/tests/py/test_email.py
+++ b/tests/py/test_email.py
@@ -66,9 +66,10 @@ class TestEmail(EmailHarness):
         msg = json.loads(response.body)['msg']
         assert msg == "A verification email has been sent to alice@example.com."
         with patch.object(self.website.app_conf, 'check_email_domains', True):
-            response = self.hit_email_spt('add-email', 'test@ipv6.changaco.net')
+            email = self.website.env.test_email_address
+            response = self.hit_email_spt('add-email', email)
             msg = json.loads(response.body)['msg']
-            assert msg == "A verification email has been sent to test@ipv6.changaco.net."
+            assert msg == f"A verification email has been sent to {email}."
 
     def test_participant_can_add_email_with_unicode_domain_name(self):
         punycode_email = 'alice@' + 'accentué.com'.encode('idna').decode()