Fix #122 -- Allow users to re-send order links (#197)

If the provided mail address has not ordered anything, there will still
be a mail generated and sent to an invalid mail address, to avoid
obvious timing attacks to determine active users.

src/pretix/base/services/mail.py

@@ -11,6 +11,7 @@ from pretix.base.models import Event, Order
 from pretix.multidomain.urlreverse import build_absolute_uri
 
 logger = logging.getLogger('pretix.base.mail')
+INVALID_ADDRESS = 'invalid-pretix-mail-address'
 
 
 class TolerantDict(dict):
@@ -53,6 +54,9 @@ def mail(email: str, subject: str, template: str,
     :raises MailOrderException: on obvious, immediate failures. Not raising an exception does not necessarily mean
         that the email has been sent, just that it has been queued by the email backend.
     """
+    if email == INVALID_ADDRESS:
+        return
+
     with language(locale):
         if isinstance(template, LazyI18nString):
             body = str(template)

src/pretix/base/settings.py

@@ -163,6 +163,18 @@ to your order for {event}.
 You can change your order details and view the status of your order at
 {url}
 
+Best regards,
+Your {event} team"""))
+    },
+    'mail_text_resend_all_links': {
+        'type': LazyI18nString,
+        'default': LazyI18nString.from_gettext(ugettext_noop("""Hello,
+
+somebody requested a list of your orders for {event}.
+The list is as follows:
+
+{orders}
+
 Best regards,
 Your {event} team"""))
     },