Proposal/Invoice can send documents via email in two different manners. You can pick the method you wish to use on the configuration form:
The default method is Direct via SMTP server.
This gives the best-looking result on the receiving end with most email programs because the email body is actually in true .HTML format, with your logo graphic encoded right in. The first time you use the method, you must specify an SMTP server:
By default, you are sent a "Blind Carbon Copy" (BCC) of the order so that you can file it in your email program's normal "send items" folder.
The other method is Use system MAPI client.
This method starts up your default MAPI system email program (such as Outlook) and adds the document and your logo graphic as attachments.