I believe this is the setting you will need to enable, in order to accomplish what you want to do.
Login as the System Administrator
Goto Security -> Antispam Administration -> Options
Put a Check mark in Disable spam filtering on SMTP whitelisted IP addresses
I believe spam checks may still run, depending on what SmarterMail version you have, they might of solved that problem recently, but in any case it won't score anything on those, so your emails will not scored as spam.
This may only apply to inbound emails, your case is probably outbound emails, this setting may not apply to that. I also noticed there isn't really an easy way to tell why an email message got put into the spam quarantine, you will have to view the logs, I believe the Delivery log. Maybe also SMTP depending.