Outlook has no size limits (except those imposed by the PST). Any limits on
incoming/outgoing mail are imposed by your ISP.
If you use Exchange as an email server in an organization then there is a
mailbox limit and likely a send/receive attachment cap as well. Any limits in
that situation is imposed at the Exchange level and is determined by company
policy and/or your Exchange Administrator.
Consider using a website such as yousendit.com or dropload.com to transfer
extremely large files. It's a quick alternative.