We recently came across this issue with one of our gravity form submission, we contacted wpengine where we host our wordpress and they are saying everything is going through well and they have shared some screenshots of the deliverability, i have attached them to this comment, this client of ours their business is mostly depended on form submissions from their customers can you tell us why has this happened only to 1 form submissions, the website this issue caused on is this https://stegallcliffordlaw.com/ and the web page where the form is Sellers/Listing Agent Request Form | Stegall & Clifford
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.