Keep in mind that freebsd-questions keeps an archive of all postings along with the e-mail addresses of the senders. I used a disposable yahoo address when I signed up, and had to dispose of it after I started receiving viruses sent to that address. It's a good idea to use disposable addresses for all communications that are archived on the web anyway.
So, in your case, I suggest that you cancel your current freebsd-questions subscription, then use Address Guard in yahoo to create an address just for that forum, making sure that you check the box to indicate that you want to be able to send messages from that address, and sign up for the freebsd-questions mailing list using the new address.
And, when you post to the freebsd-questions mailer, be very sure you're posting from the address you signed up with.