When you click the Send by Email in the Outlook Add-In for Business Central, it opens a new email in the Outlook client with the document attached. I believe this should also be the default action when you send a document from the browser version of Business Central (with an option in the setup to change if desired).

This would allow people the ability to send from their own address, rather than through the single email from SMTP as is the default today. It would also give them more control over formatting their message, and the ability to add additional attachments to the message.