Depends on the purpose of the emails.
I always exchange several emails before the meeting getting to know each other. Sometimes I communicate for several weeks with a potential client before our schedules align.We talk about interests, hobbies, expectations, exchange stories. In the end, I usually end up spending a couple of hours just writing to each suitor before the first meeting.
I wouldn't have it any other way. Then when we meet, there is a feeling of familiarity that helps build intimacy. As well, sprinkling the conversation with some flirting helps build excitement. To date, I have received the most positive feedback on this strategy from the people I've met. The fact that it helps me to sustain my minimum of several hours at the top rate for Calgary (and I do not even have the model, "perfect 10" looks) also evidences that people are willing to pay a premium for seduction.
I never send additional pictures before a date.