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2. Relay your email through a host that knows and
trusts your system. Solid DNS and mail server
skills are required by the team handling the
relay server.
3. Create a normal user account on an email server
(complete with a valid email address), and send
emails as an authenticated user through that
platform. We recommend this method since it
tends to work very well, and the requirements can be
easily communicated to the team that maintains
your email.
Pros
No configuration required on the
Asterisk server.
Relatively simple to configure on
the Asterisk server.
Easy to set up an email account for
Asterisk: you just have to create a
user on your email system named
“Company PBX” or some name
that identifies it, and then use the
credentials for this user to send all
email through.
Essentially, what you need to do is make sure the Mail Transport Agent (MTA)4 of
your Asterisk server can send email from the asterisk shell/user account. The Aster‐
isk voicemail engine will use the same mechanisms to send your voicemail to email.
For further information on the subject of MTAs, you’ll want to consult a Linux
administration book such as UNIX and Linux System Administration Handbook, 5th
Edition, or an MTA-specific title such as O’Reilly’s Postfix: The Definitive Guide.
Voicemail Storage Backends
The storage of messages on traditional voicemail systems has always tended to be
overly complicated.5 Asterisk not only provides you with a simple, logical filesystem-
based storage mechanism, but also offers a few extra message storage options.
4 Popular MTAs these days are Postfix and Exim. The ubiquitous sendmail still exists as well, although its pop‐
ularity has waned in the past few years. You’ll find Postfix on your RHEL/CentOS machines by default, and
likely Exim on your Debian/Ubuntu platforms (although Postfix is often recommended as the MTA there
too).
5 Nortel used to store its messages in a sort of special partition, in a proprietary format, which made it pretty
much impossible to extract messages from the system, or email them, or archive them, or really do anything
with them. Ah, the good old days of closed, proprietary systems. We miss ... no ... wait ... we do not miss them!
Voicemail Storage Backends
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Linux Filesystem
By default, Asterisk stores voice messages in the spool, at /var/spool/asterisk/voice‐
mail/<voicemailcontext>/<mailbox>. The messages can be stored in multiple formats
(such as wav and wav49), depending on what you specified as the format in the [gen
eral] section of your voicemail.conf file. Your greetings are also stored in this folder.
Asterisk does not create a folder for any mailboxes that do not have
any recordings yet (as would be the case with a new mailbox), so
this folder cannot be used as a reliable method of determining
which mailboxes exist on the system.
Figure 8-2 shows an example of what might be in a mailbox folder. This mailbox has
no new messages in the INBOX, has two saved messages in the Old folder, and has
busy, unavailable and name (greet) greetings recorded.
Figure 8-2. Sample mailbox folder
For each message, there is a matching msg####.txt file, which con‐
tains the envelope information for the message. The msg####.txt
file is also critically important for message waiting indication
(MWI), as this is the file that Asterisk looks for in the INBOX to
determine whether the message light for a user should be on or off.
IMAP
Some organizations prefer to manage voicemail as part of their email system. This
has been called unified messaging by the telecom industry, and its implementation has
traditionally been expensive and complex. Asterisk allows for a fairly simple integra‐
tion between voicemail and email, either through its built-in voicemail-to-email han‐
dler, or through a relationship with an IMAP server. We don’t recommend IMAP
integration simply because it’s a lot of work for very little gain, and it is out of scope
for this book.
146
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Chapter 8: Voicemail
Message Storage in a Database
It is possible to configure Asterisk voicemail to store messages as blobs within a data‐
base. This was originally seen as a simple way to allow synchronization of messages
between systems. We’ve never been fans of the idea, since databases are not designed
for bulk storage of binary data, and there are many other ways to synchronize files
across systems.