Although I do not practice law in the State of New York, the general rule is that there is a difference between "solicitation" of a crime, and actually committing a crime (in this case, patronizing a prostitute).  The crime of solicitation (which can be applied in varying criminal contexts -- it is not just limited to prostitution) involves asking someone to engage in illegal behavior.  Therefore, depending on the specific content of the emails, it is theoretically possible that one or more of them may constitute the crime of solicitation.  Although I think that it is generally unlikely that law enforcement would arrest an individual for solicitation on this basis, given the recent attention drawn to craigslist it definitely is possible.  Therefore, I recommend that whoever sent the emails consult with and/or retain a criminal defense attorney to protect his/her rights with respect to this matter from this point forward.