I reviewed the Endian documentation about the email size.
They refer only at "maximum email content size" (I think the whole email: body and attachment):
"Choose maximal email contentsize:
The maximum size allowed for a single e-mail message. Several predefined values can be selected from the drop-down menu*. Choosing the custom email contentsize option reveals the next option.
Custom maximum email contentsize (in KB):
The maximum size in mega bytes of the e-mail that will be accepted by the SMTP server."
*Drop-down menu: custom maximum email content size; 5 MB; 10 MB; 15 MB; 20 MB; 25MB; 30 MB; 35 MB; 40 MB; unlimited email contentsize.