When attempting to send mail you may receive an error "Could not instantiate mail function."  This error is the result of the server failing to process a PHP Mail() function request, which can be caused by several things, one of which being an invalid sender.  If you are receiving this error, first try setting the "System Emails From Email" under General Settings > Mail tab to a valid email address.  If this does not work, the next option will be to try using the SMTP option for "Mail Type" on the same General Settings >  Mail tab.  When using SMTP you will need to provide a valid SMTP Host, Username, and Password which can all be obtained from your email hosting provider.