Store whether we know email addresses are working because links have been clicked

src/pretix/presale/urls.py

@@ -49,6 +49,8 @@ event_patterns = [
         name='event.cart.add'),
 
     url(r'resend/$', pretix.presale.views.user.ResendLinkView.as_view(), name='event.resend_link'),
+    url(r'^order/(?P<order>[^/]+)/(?P<secret>[A-Za-z0-9]+)/open/(?P<hash>[a-z0-9]+)/$', pretix.presale.views.order.OrderOpen.as_view(),
+        name='event.order.open'),
     url(r'^order/(?P<order>[^/]+)/(?P<secret>[A-Za-z0-9]+)/$', pretix.presale.views.order.OrderDetails.as_view(),
         name='event.order'),
     url(r'^order/(?P<order>[^/]+)/(?P<secret>[A-Za-z0-9]+)/invoice$',

src/pretix/presale/views/order.py

@@ -65,6 +65,15 @@ class OrderDetailMixin(NoSearchIndexViewMixin):
         })
 
 
+@method_decorator(xframe_options_exempt, 'dispatch')
+class OrderOpen(EventViewMixin, OrderDetailMixin, View):
+    def dispatch(self, request, *args, **kwargs):
+        if kwargs.get('hash') == self.order.email_confirm_hash():
+            self.order.email_known_to_work = True
+            self.order.save(update_fields=['email_known_to_work'])
+        return redirect(self.get_order_url())
+
+
 @method_decorator(xframe_options_exempt, 'dispatch')
 class OrderDetails(EventViewMixin, OrderDetailMixin, CartMixin, TemplateView):
     template_name = "pretixpresale/event/order.html"