Safe mail marked as junk mail after every cleaning session

When I download my webmail to Outlook on my home pc (not Outlook.com but the 'old' version that comes with Office), after I have used Ccleaner - lots of safe mails suddenly end up in the junk mail folder. Every time I indicate the senders as 'safe', but after the next Ccleaner clean-up new mails from the same senders get back to being 'unsafe/junk/spam'.

Is there any way to prevent this happening again? I've gone through all the options in the free version of Ccleaner, but without any result.

Thank you.