Anything that is not text is an attachment in email. Email is a purely text medium. The attached files are converted to text, sent to a recipient, then the recipient's email client decodes the text back into a file. Sometimes, the outgoing email server or the incoming email server can "damage" the encoding while scanning for spam, viruses, etc. AOL is notorious for that.
If the attachment is displaying as embedded, that is how the recipient's email client chose to display the attachment. Outlook is notorious for this.
Try sending the email as plain text. Don't add colors, mixed fonts, or anything like that to the email--even in the signature. In the Edit menu, choose "send windows friendly..." and "Add attachment to end of message." The various versions of Outlook all have display bugs which Apple has tried to work around. Outlook is fine protected behind a corporate firewall, in an Exchange server environment, but when it has to interact with the rest of the internet, it fails miserably.
Besides deleting and readding your printer, (and maybe resetting the printing system), I don't have a Brother printer so can't offer much with that.
Is it with the Brother scanning software or with Image Capture?