Do you know where your addresses go?

Being a deliverability consultant, I end up signing up for a lot of lists and providing email addresses to a lot of different websites I may not normally trust with my email address. The only way to manage the resulting volume of email is using a disposable address system. There are a number of commercial versions, but we built our own system.
Any time I need to sign up with a client, I create a new email address. Part of the address creation process involves making notes about where and when the address was used. When mail is received at any of the email addresses I have used, that email is appended with the data I provided at the time I signed up and forwarded to a mailbox on my main system. If an address ends up compromised or sold and getting too much mail, I can just turn it off. This system allows me to freely hand out addresses, without a large amount of mail ending up in my primary mail box.
Disposable addresses great way to monitor what my clients are doing with my email address. I have found, in at least 2 cases, that my clients are doing nothing wrong, but there are leaks in their process that lets email addresses get out to spammers. My reports of data leaking were the first they knew about any problems with their vendors or customers.
I strongly recommend any marketer who shares any data, include in that data test or seed accounts. Sign up for your own lists, using unique addresses, so that you can see what kind of mail your subscribers are receiving once they sign up at your site. If you are providing data to customers or vendors, include unique test data in each list. If you start getting unexpected mail to those addresses, you can track back to the specific vendor with the data problem.
Your email address list is one of the biggest assets your company has. Protect that asset by monitoring what others are doing with it.