Is there a Limit to how many people you can send email to from Maximizer when your Mail client is Outlook 2003? (Exchange Backend)

I am not aware of any limit with regards to the number of emails that you can send. Are you having a particular problem?

If you are using the Maximizer campaign manager then it does not matter at all which email client you are using as all emails are sent through and SMTP server. Details of the SMTP server to use can be configured in the Maximizer administrator (file->prefrences->automated services).