Find a message that’s from us somewhere in your Roadrunner mailbox.
Select that message.
Click the Add Contact button. (It’s a rather small icon next to the From address.)
First, get the From address from your most recent email from us.
Click the Contacts button.
Select New Contact.
You’ll see the Brief View, which is fine for this purpose. In the space provided, type or paste the From address from your most recent email from us. Enter a Display Name to go with this Contact. (You can’t create a contact without one.)