Sender keeps appearing as Junk Mail

Sender keeps appearing as Junk Mail

I have one email sender (it's my bank) where their notification emails continuously appear in the Junk Mail folder. I have repeatedly marked the mail as Not Spam as well as adding the email address to my contacts list. The email address they send from is the same each time so I'm at a loss as to why their mail keeps going to my junk folder.

Is there anything else I can do to ensure the emails reach my inbox or is this a legitimate bug? Or is this a problem with the sender's mail server?