If your emails from AccountEdge don't have PDF attachments, security software on your computer might be interfering with the email being sent from AccountEdge to Outlook or Mac Mail. Try temporarily disabling security software (antivirus, firewall, etc.) to see if this identifies the program which might be interfering. You might need help from an IT person to resolve this issue.
As a temporary workaround, you can re-send the email from your email program's Outbox or Sent Items folder, or save the document as a PDF file and manually attach it to an email. To save a document as a PDF file from AccountEdge, display the document then click Send To and choose PDF.
Also, there is a known issue with attempting to email directly from AccountEdge to Mac Mail on Mac OS X 10.11 El Capitan. The PDF of the invoice or purchase, etc. will not be attached to the email when sending directly from AccountEdge. This only occurs in Mail and does not occur when sending emails through Outlook. An AccountEdge update is now available for this. See Emailing from AccountEdge using Mac OS X 10.11 El Capitan or later for more information.