Adds logic to send proposal notifications in batches

WIP batches tests

lib/email_digest.rb

@@ -14,9 +14,11 @@ class EmailDigest
     notifications.any?
   end
 
-  def deliver
-    if pending_notifications?
-      Mailer.proposal_notification_digest(user, notifications.to_a).deliver_later
+
+  def deliver(run_at)
+    if valid_email? && pending_notifications?
+      Mailer.delay(run_at: run_at).proposal_notification_digest(user, notifications.to_a)
+      mark_as_emailed
     end
   end
 
@@ -25,4 +27,8 @@ class EmailDigest
     user.update(failed_email_digests_count: 0)
   end
 
+  def valid_email?
+    user.email.match(/\A([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})\Z/i)
+  end
+
 end