Spam filter keeps blocking legitimate email sender

The Spam email filter is filtering mail that is not Spam from an important specific sender that sends me email alerts. I have tried marking the emails not as Spam several times, but the emails are immediately moved back into the Spam folder. I tried changing the advanced email setting to not forward any emails to Spam, but it is still moving emails from this sender to the Spam folder.  I have also tried creating an email filter rule to keep any messages from this sender and move it to the Inbox, but this did not work either.