Bump!

I was having the same problem with sending working at home but not through other connection points (notably through the phone).

I resolved this by configuring the send email account to use different smtp servers based on connection which is a choice on the third account configuration screen on the N800. Worked great for me on an ex-cingular account (now att) using the smtp address cwmx.com. I configured the smtp server to not need authentication.

My email account is through the ISP I use at home so that works fine with the smtp server associated with that account. I have not tried it with random wireless connections.

Fred