From what I've seen of the SIU email servers. We aren't allowed to sent mail via smtp.siue.edu if we are off campus conventionally. Do they require the client to use SSL to login, or something else? Because it's pretty annoying to have to find a different smtp server to use each time i come home.
Allowing usage of the SMTP server from off campus is very risky. For example, it could be used to relay spam. Perhaps you could suggest OIT allow SMTP AUTH, but it is unlikely they would do this if not already supported in the SMTP server software. I use it on my personal server (postfix) and it works great.
http://postfix.state-of-mind.de/patrick.koetter/smtpauth/
If you want to use smtp.siue.edu from off campus, you have to set your client to use SSL and password authentication.
I just use Google's SMTP server (https://mail.google.com/support/bin/answer.py?answer=13287&topic=1556). If you do a little work you can make g-mail use your SIUE address (https://mail.google.com/support/bin/answer.py?answer=20616&topic=0&type=f). You can still use Outlook or any other mail-client (https://mail.google.com/support/bin/answer.py?answer=12103&topic=0&type=f) that supports TLS.