Service messages are used to alert affected users during interruptions, information, downtime, scheduled maintenance, etc.
 
Service messages can be created from 3 different locations in More Service:

From a Request

Go to «Extra» tab
Service desk>Settings>Service message link and create a  
 
Title: The subject field from the case becomes the title of the service message. You can edit it.
Message: The text you want to send.
Groups: The user groups you want to receive this service message when logging in to user web, and with the option of receiving notification by email, will be added to "Selected Groups." 
Case ID: The field displays case ID if the service announcement was created from a case. 
Priority: If several service messages have been published at the same time, the priority will determine the order in the list displayed on user web.
Show from / to: The time frame you want the service message to appear on user web.
Working date from / to: These dates are shown in the email which is sent to users as well as shown in user web.
 
 
When you save the service announcement, you will be asked if you want to send email to affected users: