I am getting the message when trying to send a mail – Error : Mailer Error Mail: Could not instantiate mail function.
Usually you will get this error message when the phpmail function in your site server is not enabled or the email sending limit exceeds.
1) You can enable the phpmail() function in the server if it is disabled
2) You can try after some time if your email sending limit exceeds and
3) You can use SMTP instead of phpmail to send emails. See details How can I use SMTP for sending emails?