I'm not much of a Yahoo user but for those of you that may have an email account with them you may want to read about this. I really have some problems with their actions.
1. It takes away a senders right of free speech.
2. They did not make any public disclosure to their users.
3. They refuse to say who long the filters are in place.
4. This is a non standard approach and may be a way for them to make sure only their site feeds up their own ads even in people private email.

Link: http://zdnet.com.com/2100-1104-944320.html