The size limit in the email integration is 2 MB. Any message that goes over this limit, will not create a new request but will be moved into "Error" folder.
I would suggest that this limit should be configurable in the endpoint configuration. Some of our customers, if not all of them, would like to increase this limit. At the moment this takes too much manual effort from the agents, they need to manually create requests from these messages that have been discarded by the integration.
Nowadays almost every single picture taken by mobile phone is over 2 MB. If you attach this in to the message, it will never reach SMAX.