Hi Peter,
you can add all of them in a group based on the building and make a IM conference.
And send the IM.
By default there are few extensions are blocked.
More info : https://support.microsoft.com/en-in/kb/2799505
If your audio format is there, You can remove it from the filtered extension or change your audio file to a format which is not mentioned in filter.
- Muralidharan. Please mark as answer/useful if my contribution helps you.
