Can I add attachments to QuickMail emails?

There's no option to attach files to emails in Quickmail.
However, it's possible to include links to emails, like download links or links to webpages, to send files to prospects.

The file needs to be hosted on a file host (Like Google Drive or DropBox or your own website). 
You can then obtain the direct download/share link from the file host and insert it as a link to the email.

Just click the "link to" button in the email editor to insert a link.