Open Gmail
Click the gear icon
Select See all settings
Go to the Filters and Blocked Addresses tab
Click Create a new filter
Enter the email address or domain in the From field
Click Create filter
Check Never send it to Spam
Check Always mark it as important if needed
Click Create filter
Open an email from the sender
Click the three-dot menu
Select Filter messages like these
Create and save the filter
Add the sender to your contacts
Move any existing emails from the sender out of Spam
Mark the sender’s emails as Not spam if they appear in Spam