One of our upstream service providers is mitigating a DOS attack on their network which may result in delivery and notification API delays for a small subset of our customers. They are working diligently to resolve the problem and we are keeping our eye on things. We appreciate your patience during this time.
Connectivity to smtp.socketlabs.com is not affected and operating normally.
Update 2013-11-28 6:17 PM EST: We have received word from our upstream provider that the problem has been resolved.