BridgeDB email responder is not interactive

BridgeDB's email response mentions that it supports queries for ipv6 bridges and bridges with specified transports, but the rate limiting feature prevents the responder from being used in an interactive way.

We could modify the rate limiting feature to allow several requests before responding negatively.

Alternately, the first response could include a brief set of instructions only, and only apply rate limiting to subsequent queries for bridges. However, this might be confusing, especially if not all translations are initially available.