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# SMTP-based Transports

smail currently supports an SMTP driver to deliver mail over TCP connections. It is capable of delivering a message to any number of addresses on one single host, with the hostname being specified as either a fully qualified domain name that can be resolved by the networking software, or in dotted quad notation enclosed in square brackets. Generally, addresses resolved by any of the BIND, gethostbyname(3), or gethostbyaddr(3) router drivers will be delivered to the SMTP transport.

The SMTP driver will attempt to connect to the remote host immediately through the smtp port as listed in /etc/services. If it cannot be reached, or the connection times out, delivery will be re-attempted at a later time.

Delivery on the Internet requires that routes to the destination host be specified in the route-addr format described in chapter-, rather than as a bang path. smail will therefore transform user%host@gateway, where gateway is reached via host1!host2!host3, into the source-route address <@host2,@host3:user%host@gateway> which will be sent as the message's envelope address to host1. To enable these transformation (along with the built-in BIND driver), you have to edit the entry for the smtp driver in the transports file. A sample transports file is given in Appendix-.