The default attachment size is 50MB ; please note that email will convert your binary files to a BASE64 encoding which will make the email larger; a 10MB file can grow to a 30MB email. The attachment size is calculated over the email size not the file size itself.
If you have a managed dedicated server and like to see what the setting is on your server you can run the following command : exim -bP | grep message_size_limit
