I have a contact form which includes a required Email field. The form notification From Email matches the site domain, and the Reply To field is the visitor’s email address from the form: {Your Email:2}
Notification emails where the web visitor enters a gmail account cause this error: WordPress was unable to send the notification email. Could not instantiate mail function.
All other visitor email accounts work and the notifications send as expected. If I leave the Reply To field empty, the notification works.