You receive an email notification that your Outbound IP Address is blocked by Trend Micro.
Trend Micro may temporarily suspend a customer's outbound filtering services if their IP address or domain is detected having spamming activities.
To ensure that you are able to send emails, Trend Micro suggests you do the following:
Bypass the HES Outbound Services
As part of the suspension of Outbound Filtering, HES will remove the customer's mail server IP access from HES. To ensure business continuity, you can remove the smart host entry for HES and establish a different smart host or relay on your mail server by entering the appropriate IP or hostname to temporarily deliver outbound email. Refer to the article:
Check if you are using an Open Relay
Check if your mail server is an open relay. If you are using an open relay, a malicious sender will eventually find and use it to send out spam. Run test tools from outside your network or use online tools. Some online tools you can use are MXToolBox's and Mail Radar's Open Relay Tests.
Secure your mail server
Update your virus scanning and protection with the latest data files. Scan your machines for viruses, and remove any viruses found. Remove email spammers from your Active Directory list or block it on your Mail Transfer Agent (MTA).
Enable Outbound Scanning
Enable the Outbound Spam or Phishing rule on HES to help catch the spam coming from your network.Although the Quarantine Action is available for the rule, your emails will not go to End-User Quarantine if it was detected as spam, nor will it go to any other "holding/quarantine area". This is a known limitation of HES and there's no workaround for it. The only action for the rule is to use Delete Action.
For more information refer to the article: Verifying if Outbound Filtering is enabled for Hosted Email Security (HES)
Use an in-house mail filtering software
If you have a mail filtering software installed on your servers, use it to combat spam. Create rules to block the spammer on your network or activate the outbound spam rules to filter our the spam mails before it reaches HES.