As for sending, the email server makes the outbound connections to where ever it needs to to deliver the email, eg other ISP's, companies etc. It can be configured to send everything through your ISP's email server, but that's not necessary and considerably less geek-worthy.
Actually, using your ISP's mail server is better form. Yes running your own is more geeky and you still can run your own server but it should be configured to forward all outbound mail to your ISP's server. The reason for this is that some servers on the Internet do not accept mail from dialup or ADSL IP ranges (in an effort to combat spam). Bigpond.com.au springs to mind. Regards -- Oliver Jones » Roving Code Warrior oliver(a)deeperdesign.com » +64 (21) 41 2238 » www.deeperdesign.com