I suspected that it might have something to do with an SMS service.
That might be a good feature especially if notifications via text message were ever to become a feature of 3CX.
Have an option, if email notification was enabled on an extension, to select which parts of the message to include...From, To, Received, Duration, and File name. Put a tick box beside each. The subject line already sums up what the first line says..."You have received a new voicemail from ....", so that line could be dropped altogether.
Perhaps put in a suggestion at http://3cx.ideascale.com/