Several of our IPs have been listed on Spamhaus.org. We are aware of the situation and working to resolve it as quickly as possible.
Update 8:14 pm: We are working with Spamhaus.org to remove the listing
Update 8:32 pm:
The delivery issues we experienced today were the unfortunate result of several of our IPs being blacklisted on Spamhaus. The source of the problem have been identified and neutralized. The majority of the blacklisted IPs are now delisted by Spamhaus. We will be working through the night to ensure the remaining IPs are clear before tomorrow morning.
The listing resulted in an increase of bounce activity and a queue of several hours this afternoon.
We apologize for any inconvenience this has caused. If you have any questions, we encourage you to contact our Delivery team at firstname.lastname@example.org.
Update 10:34 pm: