I am looking for an inexpensive solution for OWA, ActiveSync, and Outlook Anywhere to work publicly if an Exchange Server goes down. We have two Exchange 2013 servers with all roles installed setup in DAG and using DNS RR internally. For public, mail.domain.com goes to the firewall and is NAT'd to one Exchange server. Obviously if that Exchange server goes down, so does everything publicly pointing to mail.domain.com. There are two separate public IPs for each Exchange server, so we can update the public DNS IP if there is a server issue. Not the most ideal solution. I am not thrilled with WNLB and this is a VMware environment and I have seen issues with WNLB in the past when running on VMware. Haven't tried recently, but I still would rather not use it. Cost is the biggest concern, and whatever load balancer that is used, I would prefer to run on ESXi.
I've used Riverbed Stingray before for websites. Not overly thrilled with it as I have seen issues with HTTPS when running two Stingrays in HA and a OS issue caused HTTPS to stop working and didn't fail over properly to the secondary load balancer. I always hear F5 is supposed to be one of the bests and see many people talk about KEMP with Exchange. At this point, I don't have pricing on any of them.
Right now Outlook Anywhere isn't even setup with the mail.domain.com address, but that needs to be changed. Outlook is only used internally or over VPN, but there are still plenty of users connecting via OWA and ActiveSync.