There was an error trying to send your message. Please try again later.

I get this error when submitting my contact form 7 form even if all fields are filled in

‘There was an error trying to send your message. Please try again later.’

What does the above message mean and how do I fix it?

under the ‘mail’ tab for the form in the editor, the ‘to’ field is set to [_site_admin_email]

I don’t know where to go to see what the value of this tag is. Does anyone know?