It's come to my attention, users whose email addresses are powered by Yahoo are no longer receiving our emails. Yahoo's spam filter, SpamHaus, seems to have blacklisted a range of IP addresses leased to our Internet Service Provider which includes our own. I've contacted our ISP to determine if there is anything that can be done about it.
If our ISP feels they cannot do anything about it, I'll just have to move our mail server to another server. This will take some time, so, for the moment, expect Yahoo emails not to come through.
Update: Our mail server is delivering mail to Yahoo users once again. Thank you for your patience in this matter!