The error “Could not instantiate mail function” is a server-level issue. If it has only happened one time, there may have been some connection issue. If it has happened more than once, I recommend using a different provider to send your email.
You can use a WordPress SMTP plugin with the SMTP service of your choice. Or, you can use any of our dedicated mailing add-ons, which are available to all license holders. The service you choose may have a separate charge:
If you have any other questions, please let us know.