Transports are the modules within Exim that carry out the actual deliveries. Some examples of transports have appeared in earlier chapters; in this chapter, we talk about the options that apply to all of them, and then consider each particular transport in turn. The available transports are as follows:
A transport that writes messages to local files.
A transport that generates automatic replies to messages.
A transport that delivers messages to external processes using the LMTP protocol.
A transport that passes messages to external processes via pipes.
A transport that writes messages to other hosts over TCP/IP connections, using either SMTP or LMTP.
Really a pseudotransport, because it does not actually deliver the message anywhere; instead it generates a new outgoing message (an automatic reply). It is included among the transports because its method of operation and configuration are the same, and it can include a copy of the original message in the reply.
There are several generic options that can be set for any transport, though
some of them are used almost exclusively on local transports. The only required
driver, which defines which transport is being configured. For the
smtp transport, this is often the only option you need to provide. In
Exim’s default configuration file, it is configured as follows:
remote_smtp: driver = smtp
In this case, the host to which ...