diff --git a/app/main/views/invites.py b/app/main/views/invites.py
index 43e994e06..2da96a154 100644
--- a/app/main/views/invites.py
+++ b/app/main/views/invites.py
@@ -38,7 +38,7 @@ def accept_invite(token):
 
     invited_user = invite_api_client.check_token(token)
 
-    if not current_user.is_anonymous and current_user.email_address != invited_user.email_address:
+    if not current_user.is_anonymous and current_user.email_address.lower() != invited_user.email_address.lower():
         message = Markup("""
             You’re signed in as {}.
             This invite is for another email address.
diff --git a/app/main/views/sign_in.py b/app/main/views/sign_in.py
index eb77ad7a7..20033afa0 100644
--- a/app/main/views/sign_in.py
+++ b/app/main/views/sign_in.py
@@ -40,7 +40,7 @@ def sign_in():
 
         if user and session.get('invited_user'):
             invited_user = session.get('invited_user')
-            if user.email_address != invited_user['email_address']:
+            if user.email_address.lower() != invited_user['email_address'].lower():
                 flash("You can't accept an invite for another person.")
                 session.pop('invited_user', None)
                 abort(403)
diff --git a/app/notify_client/invite_api_client.py b/app/notify_client/invite_api_client.py
index 352aaef77..a3b2589b7 100644
--- a/app/notify_client/invite_api_client.py
+++ b/app/notify_client/invite_api_client.py
@@ -9,6 +9,7 @@ class InviteApiClient(NotifyAdminAPIClient):
 
     def init_app(self, app):
         self.base_url = app.config['API_HOST_NAME']
+        self.admin_url = app.config['ADMIN_BASE_URL']
         self.service_id = app.config['ADMIN_CLIENT_USER_NAME']
         self.api_key = app.config['ADMIN_CLIENT_SECRET']
 
@@ -18,7 +19,8 @@ class InviteApiClient(NotifyAdminAPIClient):
             'email_address': email_address,
             'from_user': invite_from_id,
             'permissions': permissions,
-            'auth_type': auth_type
+            'auth_type': auth_type,
+            'invite_link_host': self.admin_url,
         }
         data = _attach_current_user(data)
         resp = self.post(url='/service/{}/invite'.format(service_id), data=data)
diff --git a/app/templates/partials/jobs/notifications.html b/app/templates/partials/jobs/notifications.html
index 70a086715..5a9c3ffd7 100644
--- a/app/templates/partials/jobs/notifications.html
+++ b/app/templates/partials/jobs/notifications.html
@@ -31,7 +31,7 @@
           </p>
         {% elif notifications %}
           <p class="bottom-gutter">
-            <a href="{{ download_link }}" download="download" class="heading-small">Download this report</a>
+            <a href="{{ download_link }}" download class="heading-small">Download this report</a>
             &emsp;
             <span id="time-left">{{ time_left }}</span>
           </p>
diff --git a/app/templates/views/check/ok.html b/app/templates/views/check/ok.html
index 792f016d1..85f79b97b 100644
--- a/app/templates/views/check/ok.html
+++ b/app/templates/views/check/ok.html
@@ -39,7 +39,7 @@
       {% if template.template_type != 'letter' or not request.args.from_test %}
       <input type="submit" class="button" value="Send {{ count_of_recipients }} {{ message_count_label(count_of_recipients, template.template_type, suffix='') }}" />
       {% else %}
-        <a href="{{ url_for('main.check_messages_preview', service_id=current_service.id, template_type=template.template_type, upload_id=upload_id, filetype='pdf') }}" download="download" class="button">Download as a printable PDF</a>
+        <a href="{{ url_for('main.check_messages_preview', service_id=current_service.id, template_type=template.template_type, upload_id=upload_id, filetype='pdf') }}" download class="button">Download as a printable PDF</a>
       {% endif %}
       <a href="{{ back_link }}" class="page-footer-back-link">Back</a>
     </form>
diff --git a/app/templates/views/dashboard/_inbox_messages.html b/app/templates/views/dashboard/_inbox_messages.html
index b46b16a8c..bba1e741d 100644
--- a/app/templates/views/dashboard/_inbox_messages.html
+++ b/app/templates/views/dashboard/_inbox_messages.html
@@ -4,7 +4,7 @@
 <div class="ajax-block-container">
   {% if messages %}
     <p class="bottom-gutter-2-3 top-gutter-2-3">
-      <a href="{{ url_for('.inbox_download', service_id=current_service.id) }}" download="download" class="heading-small">Download these messages</a>
+      <a href="{{ url_for('.inbox_download', service_id=current_service.id) }}" download class="heading-small">Download these messages</a>
     </p>
   {% endif %}
   {% call(item, row_number) list_table(
diff --git a/app/templates/views/notifications/check.html b/app/templates/views/notifications/check.html
index 19c5d34e4..a58eee691 100644
--- a/app/templates/views/notifications/check.html
+++ b/app/templates/views/notifications/check.html
@@ -53,7 +53,7 @@
         {% if template.template_type != 'letter' or not request.args.from_test %}
         <input type="submit" class="button" value="Send 1 {{ message_count_label(1, template.template_type, suffix='') }}" />
         {% else %}
-          <a href="{{ url_for('main.check_messages_preview', service_id=current_service.id, template_type=template.template_type, upload_id=upload_id, filetype='pdf') }}" download="download" class="button">Download as a printable PDF</a>
+          <a href="{{ url_for('main.check_messages_preview', service_id=current_service.id, template_type=template.template_type, upload_id=upload_id, filetype='pdf') }}" download class="button">Download as a printable PDF</a>
         {% endif %}
       {% endif %}
       <a href="{{ back_link }}" class="page-footer-back-link">Back</a>
diff --git a/app/templates/views/notifications/notification.html b/app/templates/views/notifications/notification.html
index f0ef58dba..f50a3c634 100644
--- a/app/templates/views/notifications/notification.html
+++ b/app/templates/views/notifications/notification.html
@@ -35,7 +35,7 @@
         Estimated delivery date: {{ estimated_letter_delivery_date|string|format_date_short }}
       </p>
       <p class="bottom-gutter">
-        <a href="{{ url_for('main.view_letter_notification_as_preview', service_id=current_service.id, notification_id=notification_id, filetype='pdf') }}" download="download">Download as a PDF</a>
+        <a href="{{ url_for('main.view_letter_notification_as_preview', service_id=current_service.id, notification_id=notification_id, filetype='pdf') }}" download>Download as a PDF</a>
       </p>
     {% endif %}
 
diff --git a/app/templates/views/send.html b/app/templates/views/send.html
index 0049292f6..0ab3345ca 100644
--- a/app/templates/views/send.html
+++ b/app/templates/views/send.html
@@ -40,7 +40,7 @@
     {% endcall %}
   </div>
   <p class="table-show-more-link">
-    <a href="{{ url_for('.get_example_csv', service_id=current_service.id, template_id=template.id) }}">Download this example</a>
+    <a href="{{ url_for('.get_example_csv', service_id=current_service.id, template_id=template.id) }}" download>Download this example</a>
   </p>
 
   <h2 class="heading-medium">Your file will populate this template ({{ template.name }})</h2>
diff --git a/requirements.txt b/requirements.txt
index bbc4342a4..80dff8cdd 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -20,4 +20,4 @@ notifications-python-client==4.7.1
 awscli==1.14.16
 awscli-cwlogs>=1.4,<1.5
 
-git+https://github.com/alphagov/notifications-utils.git@23.3.5#egg=notifications-utils==23.3.5
+git+https://github.com/alphagov/notifications-utils.git@23.4.0#egg=notifications-utils==23.4.0
diff --git a/tests/app/main/views/test_accept_invite.py b/tests/app/main/views/test_accept_invite.py
index ae94139c8..0ff67f30b 100644
--- a/tests/app/main/views/test_accept_invite.py
+++ b/tests/app/main/views/test_accept_invite.py
@@ -315,6 +315,29 @@ def test_signed_in_existing_user_cannot_use_anothers_invite(
     assert mock_accept_invite.call_count == 0
 
 
+def test_accept_invite_does_not_treat_email_addresses_as_case_sensitive(
+    logged_in_client,
+    mocker,
+    api_user_active,
+    sample_invite,
+    service_one,
+    mock_accept_invite,
+    mock_get_user_by_email
+):
+    mocker.patch('app.main.views.invites.check_token')
+
+    # the email address of api_user_active is 'test@user.gov.uk'
+    sample_invite['email_address'] = 'TEST@user.gov.uk'
+    invite = InvitedUser(**sample_invite)
+    mocker.patch('app.invite_api_client.check_token', return_value=invite)
+    mocker.patch('app.user_api_client.get_users_for_service', return_value=[api_user_active])
+
+    response = logged_in_client.get(url_for('main.accept_invite', token='thisisnotarealtoken'))
+
+    assert response.status_code == 302
+    assert response.location == url_for('main.service_dashboard', service_id=service_one['id'], _external=True)
+
+
 def test_new_invited_user_verifies_and_added_to_service(
     client,
     service_one,
diff --git a/tests/app/main/views/test_jobs.py b/tests/app/main/views/test_jobs.py
index 43a9c784e..2b812ca3f 100644
--- a/tests/app/main/views/test_jobs.py
+++ b/tests/app/main/views/test_jobs.py
@@ -97,7 +97,7 @@ def test_should_show_page_for_one_job(
         job_id=fake_uuid,
         status=status_argument,
     )
-    csv_link = page.find('a', {'download': 'download'})
+    csv_link = page.select_one('a[download]')
     assert csv_link['href'] == url_for(
         'main.view_job_csv',
         service_id=service_one['id'],
diff --git a/tests/app/main/views/test_sign_in.py b/tests/app/main/views/test_sign_in.py
index 6f44c8d4a..563d29751 100644
--- a/tests/app/main/views/test_sign_in.py
+++ b/tests/app/main/views/test_sign_in.py
@@ -170,3 +170,30 @@ def test_should_attempt_redirect_when_user_is_pending(
             'password': 'val1dPassw0rd!'})
     assert response.location == url_for('main.resend_email_verification', _external=True)
     assert response.status_code == 302
+
+
+def test_email_address_is_treated_case_insensitively_when_signing_in_as_invited_user(
+    client,
+    mocker,
+    mock_verify_password,
+    api_user_active,
+    sample_invite,
+    mock_accept_invite,
+    mock_send_verify_code
+):
+    sample_invite['email_address'] = 'TEST@user.gov.uk'
+
+    mocker.patch('app.user_api_client.get_user_by_email_or_none', return_value=api_user_active)
+    mocker.patch('app.main.views.sign_in._get_and_verify_user', return_value=api_user_active)
+
+    with client.session_transaction() as session:
+        session['invited_user'] = sample_invite
+
+    response = client.post(
+        url_for('main.sign_in'), data={
+            'email_address': 'test@user.gov.uk',
+            'password': 'val1dPassw0rd!'})
+
+    assert mock_accept_invite.called
+    assert response.status_code == 302
+    assert mock_send_verify_code.called
diff --git a/tests/app/notify_client/test_invite_client.py b/tests/app/notify_client/test_invite_client.py
index 94e80863d..528c74a36 100644
--- a/tests/app/notify_client/test_invite_client.py
+++ b/tests/app/notify_client/test_invite_client.py
@@ -1,4 +1,40 @@
-from app.notify_client.invite_api_client import InviteApiClient
+from unittest.mock import ANY
+from app import invite_api_client
+
+
+def test_client_creates_invite(
+    app_,
+    mocker,
+    fake_uuid,
+    sample_invite,
+):
+
+    mocker.patch('app.notify_client.current_user')
+
+    mock_post = mocker.patch(
+        'app.invite_api_client.post',
+        return_value={'data': dict.fromkeys({
+            'id', 'service', 'from_user', 'email_address',
+            'permissions', 'status', 'created_at', 'auth_type'
+        })}
+    )
+
+    invite_api_client.create_invite(
+        '12345', '67890', 'test@example.com', 'send_messages', 'sms_auth'
+    )
+
+    mock_post.assert_called_once_with(
+        url='/service/{}/invite'.format('67890'),
+        data={
+            'auth_type': 'sms_auth',
+            'email_address': 'test@example.com',
+            'from_user': '12345',
+            'service': '67890',
+            'created_by': ANY,
+            'permissions': 'send_messages',
+            'invite_link_host': 'http://localhost:6012',
+        }
+    )
 
 
 def test_client_returns_invite(mocker, sample_invite):
@@ -10,10 +46,9 @@ def test_client_returns_invite(mocker, sample_invite):
 
     expected_url = '/service/{}/invite'.format(service_id)
 
-    client = InviteApiClient()
     mock_get = mocker.patch('app.notify_client.invite_api_client.InviteApiClient.get', return_value=expected_data)
 
-    invites = client.get_invites_for_service(service_id)
+    invites = invite_api_client.get_invites_for_service(service_id)
 
     mock_get.assert_called_once_with(expected_url)
     assert len(invites) == 1