Asterisk: The Definitive Guide, 5th Edition

Chapter 8. Voicemail

Just leave a message, maybe I’ll call.

Joe Walsh

Before email and instant messaging became ubiquitous, voicemail was a popular method of electronic messaging. Even though most people now prefer text-based messaging systems, voicemail remains an essential component of any PBX.

Asterisk has a reasonably flexible voicemail system named Comedian Mail.¹ Voicemail in Asterisk is provided in the dialplan by the app_voicemail.so module.

A Caveat About Voicemail in Asterisk

The app_voicemail module is one of the oldest in Asterisk, and it suffers from many limitations, especially when compared to other modules that have enjoyed a steady evolution. The code itself is something few have the nerve to mess with, and thus new features for this module are unlikely to ever appear. You need to understand that app_voicemail doesn’t just provide a dialplan application; there are all sorts of things that have to happen to ensure this all works, such as storage and file management, interaction with the email system of the operating system, time zone awareness, file formatting, security, plus a whole basket of various parameters that might need to be set. The app_voicemail module does all of that, and as a result it ends up being a sort of kludgy subsystem (on traditional PBXs, the voicemail was in fact a completely separate machine).

Numerous attempts have been made to re-engineer voicemail, but they’ve all come up short. The reasons are simple: the level of work (and therefore cost) ...