MAPI Alternative email default for Foxy previewer means that it will use default Outlook settings to send emails. The email sent will sit in their Outlook Sent Items. SMTP/logins/passwords etc details shouldn't need to be entered as it will use the Outlook settings.
If a user doesn't have Outlook they can setup a CDO-HTML with their SMTP Server, Login, Password, SMTP port (SSL if required) and Sender Information. An example is:
SMTP Server: smtp.gmail.com
Login: Alice Smith
SMTP port: 465 (SSL if required) Tick
Sender Information: AliceSmith@gmail.com