See what the Office Team at Microsoft has to share: has used to determine the message is fraudulent. You should not interact with suspicious messages and instead should delete them.
A yellow bar at the top of the message indicates an Unknown safety level. Being marked as Unknown indicates that Exchange Online Protection has marked the message as spam. You can click the It’s not spam link in the yellow bar of a junk mail item to move the message to your inbox.
Messages from a Trusted sender display a green bar at the top of the message. These are from domains identified by Microsoft as being safe.
Messages marked with a gray safety tip indicates that the email was not filtered for spam because it is either considered Safe by the user’s organization, is on the user’s safe senders list or Exchange Online Protection marked the message as junk but the user moved it out of the junk folder to the inbox. The gray safety bar also appears when images within the message have been disabled.
All four types of Safety Tips are included in the Outlook on the web experience, whereas Outlook clients, whether desktop or mobile, will display only the Suspicious safety tip. Most messages in your inbox will not have a safety tip; we only add them when we have information users need.