There is a problem if the "From" field is not from a (sub) domain attached to the account. gmail and hotmail accounts won't do, it has to be From: xxxx@YOURx10domain.com.
Not always the case, but it seems to be the cause of some problems.
Now that you have received an answer to your question and your original problem is resolved, I am going to close this thread. If you need more help or have any additional questions, feel free to open a new support request.