Looks like SBC started blocking SMTP, Port 25, for their residencial DSL customers in the last day or so in the Richmond, CA area.
This prevents anyone using an SMTP server not on the SBC network from sending mail out.
In particular, .Mac gets broken.
To fix this, change the SMTP server port in Mail preferences to 587.
The full article on Apple's support site on troubleshooting connection timeouts, where I got the new port numbers, is here: http://docs.info.apple.com/article.html?artnum=75124