I email my therapist approximately twice a month, usually in response to an unusually difficult time for me (for example, in the case of family contact or a rupture with her) or if I am not seeing her on a regular basis. She encourages me to do so and historically I have found it very reassuring. We have both acknowledged that it has moved the work and our relationship forward.

However, it is a current great source of concern to me because she has told me that she doesn't have this kind of contact with other clients. I feel a horrible sense of collusion and "specialness" which makes me very wary.

I see you are in the UK too. Is your therapist NHS or private practice? I previously had an NHS therapist and the option of emailing them would have never even occurred to me.