Mail flow routing with BigIP 2000 load balancers

Hi Rob, we have an SMTP iApp template that's currently a release candidate, but is scheduled to become officially supported in an upcoming release: https://devcentral.f5.com/codeshare/smtp-iapp-template-early-release. The deployment guide is here: https://www.f5.com/pdf/deployment-guides/f5-smtp-dg.pdf

Although I haven't tested it with the outbound scenario, I think you should be able to use it to load balance SMTP traffic both directions, as long as both your CAS and SPAM appliance are configured to send mail to the respective virtual server addresses and accept mail from the self IP addresses of your BIG-IPs.