diff --git a/taiga/projects/api.py b/taiga/projects/api.py
index 3f256081..28ae6099 100644
--- a/taiga/projects/api.py
+++ b/taiga/projects/api.py
@@ -190,6 +190,8 @@ class MembershipViewSet(ModelCrudViewSet):
         if not object.token:
             object.token = str(uuid.uuid1())
 
+        object.user = services.find_invited_user(object, default=object.user)
+
         super().pre_save(object)
 
     def post_save(self, object, created=False):
diff --git a/taiga/projects/services/__init__.py b/taiga/projects/services/__init__.py
index 4f46c6af..236bbf54 100644
--- a/taiga/projects/services/__init__.py
+++ b/taiga/projects/services/__init__.py
@@ -35,3 +35,4 @@ from .members import create_members_in_bulk
 from .members import get_members_from_bulk
 
 from .invitations import send_invitation
+from .invitations import find_invited_user
diff --git a/taiga/projects/services/invitations.py b/taiga/projects/services/invitations.py
index 34e23010..13ca2743 100644
--- a/taiga/projects/services/invitations.py
+++ b/taiga/projects/services/invitations.py
@@ -4,5 +4,23 @@ from djmail.template_mail import MagicMailBuilder
 def send_invitation(invitation):
     """Send an invitation email"""
     mbuilder = MagicMailBuilder()
-    email = mbuilder.membership_invitation(invitation.email, {"membership": invitation})
+    if invitation.user:
+        template = mbuilder.membership_notification
+    else:
+        template = mbuilder.membership_invitation
+    email = template(invitation.email, {"membership": invitation})
     email.send()
+
+
+def find_invited_user(invitation, default=None):
+    """Check if the invited user is already a registered.
+
+    :param invitation: Invitation object.
+    :param default: Default object to return if user is not found.
+
+    :return: The user if it's found, othwerwise return `default`.
+    """
+    try:
+        return type(invitation).user.get_queryset().filter(email=invitation.email).all()[0]
+    except IndexError:
+        return default
diff --git a/taiga/projects/templates/emails/membership_notification-body-html.jinja b/taiga/projects/templates/emails/membership_notification-body-html.jinja
new file mode 100644
index 00000000..efb01532
--- /dev/null
+++ b/taiga/projects/templates/emails/membership_notification-body-html.jinja
@@ -0,0 +1,12 @@
+{% extends "emails/base.jinja" %}
+
+{% block body %}
+<table border="0" width="100%" cellpadding="0" cellspacing="0" class="table-body">
+    <tr>
+        <td>
+            <p>Hi,</p>
+            <p>you have been added to the project '{{ membership.project }}'.</p>
+        </td>
+    </tr>
+</table>
+{% endblock %}
diff --git a/taiga/projects/templates/emails/membership_notification-body-text.jinja b/taiga/projects/templates/emails/membership_notification-body-text.jinja
new file mode 100644
index 00000000..ada8a450
--- /dev/null
+++ b/taiga/projects/templates/emails/membership_notification-body-text.jinja
@@ -0,0 +1,3 @@
+Hi,
+
+you have been added to the project '{{ membership.project }}'.
diff --git a/taiga/projects/templates/emails/membership_notification-subject.jinja b/taiga/projects/templates/emails/membership_notification-subject.jinja
new file mode 100644
index 00000000..1e45591b
--- /dev/null
+++ b/taiga/projects/templates/emails/membership_notification-subject.jinja
@@ -0,0 +1 @@
+[Taiga] Added to the project '{{ membership.project|safe }}'
diff --git a/tests/integration/test_memberships.py b/tests/integration/test_memberships.py
index 148dccfd..2a2f5b35 100644
--- a/tests/integration/test_memberships.py
+++ b/tests/integration/test_memberships.py
@@ -63,3 +63,22 @@ def test_api_resend_invitation(client, outbox):
     assert response.status_code == 204
     assert len(outbox) == 1
     assert outbox[0].to == [invitation.email]
+
+
+def test_api_invite_existing_user(client, outbox):
+    "Should create the invitation linked to that user"
+    user = f.UserFactory.create()
+    role = f.RoleFactory.create()
+    url = reverse("memberships-list")
+    data = {"role": role.pk, "project": role.project.pk, "email": user.email}
+
+    response = client.json.post(url, data)
+
+    assert response.status_code == 201, response.data
+    assert len(outbox) == 1
+    assert user.memberships.count() == 1
+
+    message = outbox[0]
+
+    assert message.to == [user.email]
+    assert "Added to the project" in message.subject