Like others said, each T is different.

I actually asked my T if she reads my e-mails when I send them or right before our appt. (She's always a few mins late for our appt.) Anyways, her answer was both: she reads it as soon as she gets it, and reviews it before our appt.

And my T will NOT respond to any of my e-mails unless it's some sort of emergency.

My "guess", she has read your letter, and since you told her that you could wait till the next session, she is probably also waiting.