Log in to your Mailinblack My Protect.
Click on "Senders", then on "Add a sender".
Provide the requested information:
Status:
This indicates in which list you wish to place the sender. Therefore, it can be Authorized or Banned.
Type:
The Type allows you to specify what nature the sender corresponds to. Therefore, it can be an email address, a domain name (if your manager has given you the rights) or a regular expression.
Then click on Save to validate the addition.