Non-spam email addresses always marked as spam

Non-spam email addresses always marked as spam

Hi,

Firstly - I have lots of emails in my spam folder from the same email address. When I click on 1 of these emails and mark as 'not spam' - I get an option to 'unmark the existing tickets from this contact also as spam'.

If I check this box and then click 'ok', i'm expecting all other tickets from the same email address to be auto marked as not spam also. But this doesn't happen and the emails remain in spam. 

Am I doing something wrong here?

Lastly - how do I whitelist an email from ever going into spam?

Thanks!