How to fix: "Sender denied as sender's email address is on SenderFilterConfig list'"

If you get an error message saying "Sender denied as sender's email address is on SenderFilterConfig list'" - similar to the screenshot below, it means that the sender email address is on the Block list of the recipient's Outlook.

Solution

In the RECIPIENT's Outlook:

Right click on any email in your Inbox

Choose Junk > Junk E-mail Options...

Click on the Blocked Senders tab

Click on the problematic email address

Click Remove 

Click OK

Sending should work fine after this.