Amazon Workmail - Seems like all my emails are hitting firewalls and getting rejected

Hi there, Every time I try send an email, I get the following response from a firewall:

"Technical report: Reporting-MTA: dns; a10-27.smtp-out.amazonses.com

Action: failed Diagnostic-Code: smtp; 554 bosimpinc03 bizsmtp Connection refused. 54.240.10.27 is blacklisted. Status: 5.3.0"

Seems like the workmail IP address is blacklisted. How can I get this fixed so I can respond to emails. I'm sure you can appreciate the urgency of this matter.