The junk email folder should be used by O365 to provide user-level filtering. I learned recently during a support case with O365 that the cloud Exchange service does not "learn" from items that people move into their junk email folder what content an individual user considers spam or phishing or malware. It appears that moving things to junk is the same as moving it to the deleted items folder. This is a serious omission. The junk folder should be used to analyze content or other factors that a user considers spam and filter accordingly. Using the tenant wide spam and phishing tools available to admins is not specific enough. Viagra email might be spam to most women, but if your doctor's email about your Viagra prescription gets filtered out, men might have a different opinion.