Image Sizes

This is less of a Corel question and more of a general question in the realm of email, computers, and servers. Im more knowledgeable in the design/ artistic stuff so im kind of baffled with this failed to deliver email.

This what the email I received when it failed:

"message size 1306854 exceeds size limit 1048576 of server."

Im assuming there's a general unit of measurement for file size in emails, but idk know it and these are just wacky numbers from my perspective. And I need to send this file to a client ASAP.