You should consult with an employment attorney. The answer to this question is dependent upon a few things that will require a dialogue.
The answer depends on the language of the non-disclosure agreement you signed and the contents of the email you showed the client. You should retain the services of an employment attorney if you are concerned.
The information provided above is for general purposes only. It does not constitute legal advice or create an attorney-client relationship. Seek competent legal representation, because the facts of each case are different.
Unfortunately we do not have all the information we would need to provide you a complete answer, I would suggest contacting an experienced employment attorney near you.
This answer does not constitute legal advice and you should contact an attorney to confirm or research further any statements made in this answer. Any statements of fact or law I have made in this answer pertain solely to New York State and should not be relied upon in any way in any other jurisdiction. Additionally, we also encourage you to reach out to us via Twitter (https://twitter.com/#!/WhiteRoseMarks) or Facebook (http://www.facebook.com/WhiteRoseMarks) if you have follow up questions as we do not monitor questions after providing an initial answer.
As others have stated, it is difficult to determine if what you did violates your non-disclosure agreement without seeing the agreement or your e-mails. I would suggest you send those items to an experienced employment attorney that offers a free consultation as many of us do and you can get a better answer.