E-Commerce Configuration Guide : Site Configuration Settings : Email Settings : MailAttachment
 
MailAttachment
Key value:
Any valid filepath and name within the web application’s root
Description:
A static e-mail attachment may be specified. If the file doesn’t exist or is inaccessible, the mail is still sent without the attachment. Use MailAttachment to specify a file (and path within the web application’s root) to attach to a confirmation e-mail.
Note: Limitations on e-mail size is dictated by the e-mail servers on both the transmitting and receiving ends and is not set by E-Commerce module, so including an e-mail attachment with your confirmations must take these limitations into consideration.
See also:
None