This forum is for Sage 50 Canadian, is that what you're using?

Normally Sage 50 Canadian appends the invoice number to the filename of the .FRM invoice template for an attachment filename, and there's no 'Updated' in the subject line, and you can edit the subject line and body of the invoice before sending. 

The U.S. 'Peachtree' software is only similar in a Word vs. WordPerfect convergence sort of way.

Yes it is Canadian. Sorry i meant to say that the file name for the attached invoice says "updated invoice." 

Ah, not the subject line then. 'updated invoice' comes from the filename of the .frm invoice form file when you saved it in the Forms Editor.

You could copy / paste / rename that invoice form file in Windows Explorer, then change the Reports and Forms setting in Sage 50 for the invoice.  Or use Save As in the form editor.   A good filename to use is a shortened Company name, so the emailed attachment is named something like Company_123456.

We dressed up our emailed invoice to be in colour with the company logo, but kept the default print invoice plain to save toner by not printing a blackish-grey blob that the logo became.  And added fax and email contact info.