Update:  The networking issue was resolved around 11:15 PM ET US

There looks to be a Networking issue in our Chicago Data Center, starting around 8:50 PM ET US:

Affected Components: 
1) cloudb.spamtitan.com and cloudc.spamtitan.com 
==> Related to MX records cloud1.spamtitan.com/cloud2.spamtitan.com 
==> cloudd.spamtitan.com is processing mail. 

2) cloud-out-a.spamtitan.com 
==> cloud-out-b.spamtitan.com is still processing mail.