Email is by default in the clear. As Edward Snowden said at his address at SXSW, we need to raise trust in our means of communications. If you don't do it for you, do it for the people you deal with. Encrypt your email!! Are you making it easy enough for your users to encrypt data?
TLS is completely transparent when use and provides a first layer of defence. It should be deloyed and used when possible. Full content encryption for sensitve content no longer requires deep user training or desktop software. It is also cheap enough that it can be installed and available for everyone in your organization to use, without making any impact on your budget. Let's talk about encyption.