This is not an issue, the email is blocked because the sender IP is listed in the Quick IP List (QIL). See Blocked Message Details for more information.

If the user confirms the validity of the sender IP and wants to receive such emails, below is the workaround:

1. Add the sender's email address or domain into the Approved Sender List to bypass the QIL, Known Spam Source List (KSSL), and anti-spam checking. Refer to Configuring Approved and Blocked Sender Lists.
2. Add the sender IP into the IP reputation approved list. 
   • For Trend Micro Email Security, user may decide to bypass IP reputation check only or both IP reputation check and anti-spam check. See About Approved and Blocked IP Addresses.
   • For Trend Micro Hosted Email Security, the sender IP will bypass the IP reputation checking. See About Approved and Blocked IP Addresses.
3. Submit a request to remove the sender IP from the QIL List. Visit Email Reputation Services to check the IP address reputation and follow the procedure in this article: ERS Look UP IP Addresses.