... and for what it’s worth, e-mail is not an altogether-bad way of accepting requests for certain things. But you probably should design your system from the outset with the notion that it may one day have to support both an e-mail based and a web-site based request entry system.
Depending on the exact nature of the system, it might make sense to conceptualize it as three stages: order entry and queueing; order processing; and response delivery. Perhaps these are three separate modules, designed to be run either sequentially or in parallel. Then, if “the money starts flowing in by email” and you are asked to develop a compatible order entry and queueing interface that is a web-site, you’ll be that much ahead of the game. (Forewarned is forearmed.)