Pretty much what it says!

I have a problem with my VPS not being able to send any emails to Yahoo! addresses. Each time someone with a mail account tries to send something to a Yahoo! address, the email stays stuck in the mail queue and a 'delayed mail (still trying)' message is sent back to the user.

I understand that Yahoo! has a tendency to block mail servers on a whim, but what I'd like to know is, how can I prevent Postfix from specifically retrying to send emails to Yahoo! mail servers? I don't want to stop retries to other mail servers.

I'm using Webmin, so if anybody's able to supply specific instructions on how to do it from there, that would be brilliant, but I'll be quite happy with trying to fix this from the command line right now.

Anybody? Could really do with a push in the right direction...