In most business environments, email can present many security risks. If there’s a line of communication between people who make decisions, then that line of communication can be exploited by criminals. Usually, this is done by spoofing their email address to make it appear like their message is coming from someone within the company. The email sent might attempt to get you to send them money, click on a link that reveals information, or download a virus.
Office 365 has an adjustable spam filter that you can set to be more strict with its filtering. At each increased level it uses more criteria to determine which emails are spam. However, the more strict the spam filter gets, the more emails it’ll filter out email that perhaps shouldn’t be filtered.
What To Do About Risk
All users of any email service should be cautious with all emails that they receive. Pay attention to the address the email came from, not just the name displayed. Don’t click on any links or downloads in even slightly questionable emails.
If something seems like it’s from someone you know, but you’re unsure, the best thing is to contact the sender. Ask if they sent it. There will never be a perfect solution to blocking all malicious emails, so careful use is very important.