Large store owners often set up their store with SMTP mail function to improve mail delivery rate and avoid spam problems.
This function works well in most sites, but sometimes, this can conflict with server configuration and results in an error.
“Error: RCPT TO not accepted from server! in system/library/mail.php” is one such reported issue by Opencart store owners when they send message from contact forms or feedback forms.
As a part of our Outsourced Technical Support for webhosts, we routinely resolve such errors faced by website owners.