Folks were posting earlier today noticing problems delivering to Barracuda hosted services. The good news is Barracuda has been updating their status page. As of now, the status page says things are improving.
Monitoring – Since 7PM PDT 11/1/2016, the Barracuda Essentials for Email Security service has been experiencing a sustained and unusually large number of inbound connections from unverified sources. This resulted in some customers experiencing delays in email delivery and issues accessing the message/quarantine logs. We have made significant progress sanitizing these connections. At this point, email processing capabilities have returned to normal and backlogged messages are being delivered. Also, access to the message and quarantine logs is fully restored. We are continuously monitoring the connection load, taking further steps to mitigate the impact and tracing the root cause. Our priority is to restore the service to full capacity. We will provide more information through the course of the investigation. Thank you for your patience.
There have been a lot of attacks over the recent past, some against mail servers some against other systems. There’s not enough data to know if this is related to any of that but it’s certainly worth paying attention to.