Simply add their email address or domain names to the EmailUnlimited Competitor Blocker.

In the EmailUnlimited Main Screen, go to Tools/Competitor Blocker... and the Competitor Blocker Dialog will open:

Now all you need to do is enter the email addresses of your competitors into the entry field and click on the "Add to List" button to add them to the Competitor Blocker (alternatively, you can also hit Return on your keyboard to add an item).

Not only can you block single email addresses, you can also block complete domains: simply enter the domain name of your competitor. For instance, if your worst competitor is Microsoft, enter microsoft.com.

You may even block email addresses that contain certain keywords. For example, if you do not want EmailUnlimited to send emails to obvious abuse addresses such as abuse@abc.com, simply add the keyword 'abuse' to the list of blocked addresses, and EmailUnlimited will never send any emails to email addresses that contain the term 'abuse'.

If you want to remove an item from the list, select it and click on the "Remove" button.

Click on Ok to save changes when you are finished.

Now EmailUnlimited will refuse to send any emails to all addresses that match the criteria listed in the Competitor Blocker.