We are looking at an issue with the mail delivery. Specifically, the email server appears to have an issue in accepting incoming connections. We are rebooting the server now to bring it back online and then will work to find the underlying issue.
Update: The issue has been resolved.
This issue existed for about an hour, from 3PM EST-4:13PM EST. Note that this issue is unrelated to the database server issue earlier in the week. We are still looking into the root cause for this issue.