If you are using Google Apps (or it's little brother Gmail), you can follow the "Multiple Choice" questions at:
For those wanting the quick answer...
Outgoing Mail (SMTP) Server - Requires TLS
- smtp.gmail.com
- Port: 465 or 587
- Requires SSL: Yes
- Requires authentication: Yes
- Use same settings as incoming mail server
Not using Google Apps?
If you are not using a hosted email service (e.g. if it's on the exact same server as your website), it's recommended that you use your ISP's SMTP settings.
- BigPond / Telstra (including Telstra mobiles)
- SMTP server: mail.bigpond.com
- SMTP server: mail.optusnet.com.au
(More coming soon!)