People usually break up for a reason, and so the chances of getting back together with an ex depend on whether the issues that led to the breakup have been resolved.
When a person starts dating someone new, their success in having found another appealing person to date can help them feel better about their romantic prospects.
It can be very heady to have an ongoing email chat with someone who is focused entirely on you.
In fact, this is a great sign that the person on the other end of the conversation is truly interested and invested in learning more about who you are.
Basically, our emotional and attachment needs are hydraulic: The more we rely on one individual to meet these needs (e.g., an ex-partner), the less we tend to rely on another individual to meet these same needs (e.g., a new partner). It really depends on whether the rebound relationship is better than the relationship that was left behind.
The answer to this question is a bit more complicated.