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.
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
Sending should work fine after this.