You can create custom mail filters from Cpanel -> Mail -> E-mail Filtering.
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User lever filtering
E-mail filtering allows you to select
messages that contain certain strings of text or other symbols, and
either discard them, or send them to another e-mail box of your choice.
Step 1: To access the user level filtering menu, click on the User Level Filtering icon on the main screen of your cPanel interface.
Step 2: Click on Manage Filters next to the account for which you wish to add filters.
Step 3: To add a filter, click on Create a new Filter.
Step 4: In the Filter Name field type in a unique name for the filter.
Step 5: From the Rules options you should choose the rules a mail should match in order to be filtered.
Step 6: From the Actions drop-down menu you should choose what action should be performed when a mail matches a rule in the filter.
You can add additional rules and actions by clicking the + button next to each rule and action. You can remove rules and actions by clicking the - button next to each rule and action
Step 7: To enable the filter, click on Activate.
Account level filtering
Account
level filtering is the same as user level filtering, with the only
difference that the filters created here are applied globally for the
whole cPanel account.
Type a message in the Filter Test box and click on Test Filter to see where the message will go. Use the word(s) from your filter(s) in this message to test if they work.
Please note that e-mail filtering does not leave a copy of the e-mail in the box you apply the filter for.