The priority levels set to a message allow recipients to define if one received message is at a high, or normal, or low importance level. It means that when a message is set at the high priority level, its recipients need to read as soon as possible.
This useful tool can be done with a few clicks when you are composing a new message.
Set a priority level for your composed message
1. Click 
in the Compose New Message form.
2. Select your preferred priority from the drop-down menu.
Low: The exclamation icon corresponding to the mail is marked in grey in the
column.Normal: There is no the exclamation icon. By default, the message is sent with the Normal priority.
High: The exclamation icon is marked in red.