Attachment size limitation

I searched the support site and couldn’t find any specific information on a limit to the attachment size for emails being sent and received. Does anybody have a link to this information? I am receiving the following error when I try to send an email with a large attachment.

[SMTP]Cannot send message (‘From’ field address ‘email_address_removed’ not accepted due to the following reason:
"5.3.4 Message size exceeds fixed limit

It’s currently set to 50mb

Why limit attachment size at all? I realize most other email hosts can’t handle really large attachments, but shouldn’t maximum attachment size be left to the user to decide?