Update 4/2 12:21PM
We have successfully petitioned Comcast to take our mailserver off of their block list. If you're still having issues sending to Comcast, feel free to submit a trouble ticket or contact support toll-free at (877) 720-0483

A number of clients have contacted us regarding failed mail deliveries to Comcast accounts. If you're having trouble sending to Comcast, and you get a message that looks like this:

Failed to deliver to 'xxxxxxx@comcast.net'
SMTP module(domain comcast.net) reports:
return-path address 550 216.168.37.34 blocked by ldap:ou=rblmx,dc=comcast,dc=net -> BL003 Blocked for spam. Please see http://www.comcast.net/help/faq/index.jsp?faq=SecurityMail_

be advised that we are aware of the issue, and are currently attempting to work with Comcast to resolve it as quickly as possible.

Updates will be posted to this page.