You need some sort of custom code or addin yes, Outlook doesn't do that on
its own.
Take a look at the Utilities pages at www.slipstick.com for various addins
that support sending emails for reminders.

Signature
Ken Slovak
[MVP - Outlook]
http://www.slovaktech.com
Author: Professional Programming Outlook 2007.
Reminder Manager, Extended Reminders, Attachment Options.
http://www.slovaktech.com/products.htm
>i want to send email reminders to people in my contacts folder when a
> subscription becomes due.
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>
> thanks