At approximately 4AM EST we have noticed a failure in updates from one of our AV vendors. That failure produced higher than expected virus matches which ended up queuing a larger than normal amount of messages. We have resolved the issue with the update and are currently re-processing all the mail that was quarantined over the past few hours.
Please stand by, we will deliver all mail.
Update: 7:29 AM EST: Nearly all the mail that was affected by the faulty AV update has been processed and has been dispatched to delivery queues. As of the previous update, all new mail has been delivered in realtime. It is important to note that we are only processing the backlog for the messages that did get trapped by the faulty AV update.
Update: 9:15 AM EST: 99% of the messages have been flushed out. By the time you read this posting all the mail would have been delivered. No mail has been dropped during the period, if you experience further issues with delays please follow our deployment guide and support documentation, we find most delays are related to the on-premise issues relating improper firewall configuration, connection rate limiting (by far) and other SPAM/malware scanning that does not properly whitelist ExchangeDefender systems.