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<TITLE>Exim Specification - 12. Driver specifications</TITLE>
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<H1><A NAME="SEC397" HREF="spec_toc.html#TOC397">12. Driver specifications</A></H1>
<P>
<A NAME="IDX1013"></A>
The second, third, and fourth parts of Exim's configuration file specify which
transport, director, and router drivers are to be used. Directors and routers
are similar, in that an address is passed to a list of them in the order in
which they are defined, whereas the order in which transports are specified is
immaterial, because a transport is invoked only after being passed an address
by a director or a router. Section 3.4 discusses how the different
kinds of delivery driver interact.
</P>
<P>
The seventh part of the configuration file (if present) specifies the
authenticators that are to be used for SMTP connections (see chapter
35). These are a somewhat different kind of `driver' to the others,
but they are configured in a similar way.
</P>
<P>
The format of the configuration data is the same for all four types of driver,
and is as follows:
<PRE>
<<EM>instance name</EM>>:
<<EM>option</EM>>
...
<<EM>option</EM>>
</PRE>
<P>
<A NAME="IDX1014"></A>
<A NAME="IDX1015"></A>
There are two kinds of option: <EM>generic</EM> and <EM>private</EM>. The generic
options are those that apply to all drivers of the same type (that is, all
directors, all routers, all transports or all authenticators).
There is always at least one generic option, called <EM>driver</EM>, which specifies
which particular driver is being used.
<A NAME="IDX1016"></A>
The private options are particular to each driver, and none need appear.
</P>
<P>
The options may appear in any order, except that the <EM>driver</EM> option must
precede any private options, since these depend on the particular driver. For
this reason, it is recommended that <EM>driver</EM> always be the first option.
</P>
<P>
In earlier versions of Exim, commas were used between options, and the generic
options had to precede the private ones and be terminated by a semicolon. This
has not been the case for some time, and at release 3.00 the
backwards-compatibility code for ignoring commas and semicolons was removed.
</P>
<P>
Each instance of a driver is given an identifying <EM>instance name</EM> name for
reference in logging and elsewhere. The name can be any sequence of letters,
digits, and underscores (starting with a letter) and must be unique among
drivers of the same type. A router and a transport (for example) can each have
the same name, but no two router instances can have the same name. The name of
a driver instance should not be confused with the name of the underlying
driver. The configuration lines
<PRE>
remote_smtp:
driver = smtp
</PRE>
<P>
create an instance of the <EM>smtp</EM> transport driver whose name is <EM>remote_smtp</EM>.
The same driver code can be used more than once, with different instance names
and different option settings each time. A second instance of the <EM>smtp</EM>
transport, with different options, might be defined thus:
<PRE>
special_smtp:
driver = smtp
port = 1234
command_timeout = 10s
</PRE>
<P>
The names <EM>remote_smtp</EM> and <EM>special_smtp</EM> would be used to reference these
driver instances from directors or routers, and would appear in log lines.
</P>
<P>
Comment lines may appear in the middle of driver specifications. The full list
of option settings for any particular driver instance, including all the
defaults, can be extracted by making use of the -<EM>bP</EM> command line option (see
chapter 5).
</P>
<P>
The next chapter describes the environment in which local deliveries are done,
and how this is affected by the configurations of the relevant directors,
routers, and transports. Then there is a chapter describing the generic options
for transports, followed by descriptions of the available transport drivers.
Directors and routers have some generic options in common, and these are
covered in chapter 20 before the descriptions of the generic
options that are specific to each type of driver, and the drivers themselves.
The SMTP AUTH mechanism for client authentication is described in chapter
35, which is followed by descriptions of the available
authenticators.
</P>
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