I was wondering if there is a to tell Outlook 2003 only to send x Mails per Minute or something, because right now, when sending to multiple (lots of) recipients, I get:
Policy Rejection- Too much mails in timeframe
You'll have to use fewer recipients at a time. Many email services have limits: per message, per hour or per 24 hour period. Outlook does not have a timer, as far as I know.
A commercial solution: Batched Mail component (single user license €24) :
At the present moment more and more mail servers impose limitations on the number of outgoing messages sent during a certain period of time. It is done in order to prevent undesirable mass mail distributions. But as well as any other security measures, this restriction brings inconvenience to those users, who send a bulk of mail daily. The use of the Batched Mail allows you to plan the mail sending process. This Microsoft Outlook add-in sends a specific amount of mail during an hour or with a specified delay between sending two messages that go one after another.
Why don't you set an option to defer the mail to be sent by few minutes. You can find the steps on how to do it here http://www.howtogeek.com/howto/microsoft-office/use-outlook-rules-to-prevent-oh-no-after-sending-emails/
Don't know if this is what you are expecting.