For extension voicemail, extension users can choose how to play greetings in different presence: Default greeting: Play a greeting for any presence that doesn't have a personal greeting. Presence greetings: Play a personal greeting for each presence (available, away, do not disturb, lunch break, business trip, and off work).
After helping tens of thousands of companies set up voicemail systems, we’ve learned that there is no set of rules defining what makes a great business voicemail, but there are definitely some key points that you should aim to hit. Before you hit the record button for your voicemail message, take some of these tips into account:

Skype for Business calls your voicemail and guides you to record a personal greeting.
Rehearse or write down your message before recording it. Remember that old saying “practice makes perfect?” It’s certainly true when it comes to creating an electronic greeting. The more you’ve rehearsed, the easier the message will be to restate. If you don’t have time to practice, writing down the greeting before recording it – and then reading it aloud from the paper – may help you stay focused on the correct wording.