2. Create a text file with a short path location - example c:\filter\filter.txt
3. Create Global Black list rule
Action - Reject
Item - Sender
Function - Contain string from file
String - c:\filter\filter.txt
4. Create content filter
Where Remote IP address matches
Contains string separated with semi-colon
Where Recipient matches email@example.com
Add %%subject%% to a file
Filename - c:\filter\filter.txt
Text - %%subject%%
If you have an internal network it is best to apply this rule to your private network subnet to help avoid abuse. The string for Remote IP address should match your private network range, do not use the * wildcard when using function Contains string separated with semi-colon, for example use, 172.16.0., or 10.0.0., or 192.168.1.
When someone sends a message to firstname.lastname@example.org
the content filter will add the content of the subject to the filter.txt file. Make sure your users understand they need to put only an email address in the subject.
Once the content filter adds the email address to the filter.txt file the email addresses read from this file will be rejected by the Black list rejection rule.