This is actually an awesome KB article. It mostly only applies to people using the NA NOC ... but still a good read. Frankly, I never tell anyone to use a proxy for BES SRP connectivity (mostly because it adds another layer of complexity to something that people already don't usually understand) ... but if you're using / need to proxy SRP connections, here are two supportable ways to do it:

KB19236 - Recommended configuration for SRP connections through a proxy ...