Make sure the MX record is entered exactly as provided in the Hosted Email Security welcome email message.
An MX record (DNS mail exchanger host record) determines the message routing for all messages sent to a domain. To route messages destined for your domain through the Hosted Email Security MTA, you must point your MX record to the fully qualified domain name (FQDN) provided in the welcome email message that Trend Micro sent you after you registered.
To disable Hosted Email Security, point your MX record to route all inbound SMTP traffic to your own mail server.
If you are unsure how to configure the MX records for your domain, contact your Internet Service Provider or your DNS technician.
The following external links to MX record configuration help pages are provided for your convenience: