To answer part of the question an email could have served as notice to withdraw an offer but, to terminate the contract you must show just cause.
In your case now with more information, I would seek the advise of an attorney since you do not have an agent representing you.
Next time, I would seriously consider working with an agent. They are free to use in most cases and have been trained to deal with this sort of problem.
Penney, do you mean writing an email is enough to release the seller and buyer? Is it not required to complete and send 'Notice to Seller...Terminating Contract' document to release the seller?
Please consult your buyer's agent on this as this would be their job to do.
There may be more steps that need to be taken but it is hard to tell with your post.