A: Enable junk filter. Find out more: Junk Filtering Setup (Users)
A: Your email address is like an online equivalent of your home address or phone number - once you give it to anyone, it is impossible to stop getting calls/letters/emails, even if they were spam. Find out how spammers get your email address.
A: Add the sender's address into your Address Book, and turn on the “Sender is in my Contact list” option.
A: Increase the level of sensitivity, set it to “high” to see if that improves your junk filtering.
A: Use “blacklist” to block those email. Go to Email > Configuration > Options > Black list to add the sender's email into black list, or click “Block” while you are reading the email in webmail. Learn more: Blacklist a Sender Email Address on your Webmail
A: Chose “Delete immediately” on your junk filtering setting. Or you can setup your mail client to download the junk mail from time to time. Refer to: Getting email from junk folder on Ms Outlook
A: If you see “Junk Mail settings has enabled on the domain level, you are not allow to change it here.” on your junk setting, it means your administrator has turned on the Global Junk Control. The global setting will override your junk setting.