BIG IP to load balance mail servers?

with no Port or Address Translation

 

 

You probably need to leave address translation enabled. In most LB scenarios, address translation (which in this case refers to destination address) is required: LTM accepts the traffic on the virtual address, then proxies to the real address. In your case, port translation doesn't matter since both VS and pool members are listening on the same port.

 

 

HTH

 

/deb