ServiceDesk allows users to send notifications to specific users or members of specific groups or roles when an escalation action expires. These notifications are written by the System Administrator in Plain Text. Some time ago an enhancement was introduced to have these messages sent in HTML format so they could appear more appealingly. In order to achieve this an option was added to the 'Outbound Mail Server Settings' in the 'Mail' component called 'Send Mail as HTML'.
When the 'Send Mail as HTML' checkbox is selected all the Outbound mail is sent in HTML format. This is usually fine as if you are using this feature you will have it in conjunction with HTML fields on your objects so they are already formatted. However, some outbound mail, and most noticably, Escalation notifications can not have an 'HTML' field so the formatting that worked before 'Send Mail as HTML' was turned on no longer works.
This is quite simple to work-around, the notifciations just need to have relevent HTML inserted. For example, if you want to have a line break you will need to add <p> or <br>. If you want to make words more prominent you may want to put <strong> before them and </strong> afterwards to have them appear bold. For users familiar with HTML any HTML/CSS formatting can be applied to the notifications to make them appear exactly as you wish.