diff --git a/static/js/landing-page.js b/static/js/landing-page.js
index eda8622ee6..ecc0b7d7c4 100644
--- a/static/js/landing-page.js
+++ b/static/js/landing-page.js
@@ -40,7 +40,12 @@ $(function () {
             $("#success").show();
         },
         error: function (xhr, error_type, xhn) {
-            $("#error").show();
+            if (xhr.status === 403) {
+                // You tried signing up with a domain that already uses Zulip!
+                $("#group-already-uses-zulip").show();
+            } else {
+                $("#error").show();
+            }
         },
         complete: function (xhr, statusText) {
             $("#beta-signup").removeAttr('disabled').text("Sign up");
diff --git a/templates/corporate/signup.html b/templates/corporate/signup.html
index 23dc4c382d..b5bf7820db 100644
--- a/templates/corporate/signup.html
+++ b/templates/corporate/signup.html
@@ -28,6 +28,15 @@
         While you wait, check out some of our <a href="/features">features</a>!
       </div>
 
+      <div id="group-already-uses-zulip" class="alert alert-hidden alert-success alert-block">
+        <p>Good news: your group already uses Zulip! We've sent you an
+          email with the steps to complete your registration.</p>
+
+        <p>(If you want to create a new group instead of joining this one,
+          please contact <a href="mailto:support@zulip.com">support@zulip.com</a> and we'll
+          get you set up)</p>
+      </div>
+
       <div id="error" class="alert alert-hidden alert-error alert-block">
         <h4>Ruh-roh!</h4>
         Hmmm, something went wrong. Please send email to <a href="mailto:support@zulip.com">support@zulip.com</a>.
diff --git a/zerver/views/__init__.py b/zerver/views/__init__.py
index 57f7e99878..27b9169aff 100644
--- a/zerver/views/__init__.py
+++ b/zerver/views/__init__.py
@@ -201,17 +201,32 @@ def principal_to_user_profile(agent, principal):
 @has_request_variables
 def beta_signup_submission(request, name=REQ, email=REQ,
                            company=REQ, count=REQ, product=REQ):
+
+    domain = resolve_email_to_domain(email)
+    realm = get_realm(domain)
+
     content = """Name: %s
 Email: %s
 Company: %s
 # users: %s
 Currently using: %s""" % (name, email, company, count, product,)
+
     subject = "Interest in Zulip: %s" % (company,)
+    if realm:
+        subject = "(Realm already exists) " + subject
+
     from_email = '"%s" <zulip+signups@zulip.com>' % (name,)
     to_email = '"Zulip Signups" <zulip+signups@zulip.com>'
     headers = {'Reply-To' : '"%s" <%s>' % (name, email,)}
     msg = EmailMessage(subject, content, from_email, [to_email], headers=headers)
     msg.send()
+
+    if realm:
+        # This domain already uses Zulip, so they probably meant to
+        # register. Send them a registration link.
+        send_registration_completion_email(email, request)
+        return json_error("Your group is already signed up!", status=403)
+
     return json_success()
 
 @require_post
@@ -698,16 +713,23 @@ def accounts_home_with_domain(request, domain):
     else:
         return HttpResponseRedirect(reverse('zerver.views.accounts_home'))
 
+def send_registration_completion_email(email, request):
+    """
+    Send an email with a confirmation link to the provided e-mail so the user
+    can complete their registration.
+    """
+    prereg_user = create_preregistration_user(email, request)
+    context = {'support_email': settings.ZULIP_ADMINISTRATOR,
+               'enterprise': settings.ENTERPRISE}
+    Confirmation.objects.send_confirmation(prereg_user, email,
+                                           additional_context=context)
+
 def accounts_home(request):
     if request.method == 'POST':
         form = create_homepage_form(request, user_info=request.POST)
         if form.is_valid():
             email = form.cleaned_data['email']
-            prereg_user = create_preregistration_user(email, request)
-            context = {'support_email': settings.ZULIP_ADMINISTRATOR,
-                       'enterprise': settings.ENTERPRISE}
-            Confirmation.objects.send_confirmation(prereg_user, email,
-                                                   additional_context=context)
+            send_registration_completion_email(email, request)
             return HttpResponseRedirect(reverse('send_confirm', kwargs={'email': email}))
         try:
             email = request.POST['email']