I have an SBS2003 server using bizmail.yahoo.com as the mail server. It stopped sending mail last Friday (although it still receives). My end-users use Outlook with only the exchange server account set up. Pop3 settings are managed using the POP3 connector manager.
When I called their ISP for support, they only seem to be familiar with setting up POP mail on workstations, not servers, but they were able to confirm that they had made both a port change (from 25 for outgoing mail to 465) and that they were now requiring a secure connection (SSL). I opened my SMTP virtual server properties box, and can see where to change the outbound connection from port 25 to 465, but I am unsure where exactly to set the secure connection. Under outbound authentication I can set basic authentication (I would assume this would use the core email account username and password), integrated windows authentication, or TSL encryption. TSL encryption looks like the safest bet, but SBC-Ameritech could not confirm for me whether this is the same as their required 'secure connection (SSL)' setting.