Emails sent through web hosting servers ensure reliability and deliverability, as they leverage the host's infrastructure and established reputation to bypass spam filters. This method provides professionalism by allowing for a custom email address, which builds trust and brand recognition. Using hosting servers for email also offers better control and security, with features like enhanced filtering and regular backups managed directly within the hosting environment.
This most likely means that the user is blacklisted.
Please submit a ticket to our technical support team and include the full bounce back message with the full headers to fully investigate the problem and provide a complete resolution.