Postfix (NNCP)

This section is taken from Postfix and UUCP manual and just replaces UUCP-related calls with NNCP ones.

Setting up a Postfix Internet to NNCP gateway

Here is how to set up a machine that sits on the Internet and that forwards mail to a LAN that is connected via NNCP.

You need an nncp-exec program that extracts the sender address from mail that arrives via NNCP, and that feeds the mail into the Postfix sendmail command.
Define a pipe(8) based mail delivery transport for delivery via NNCP:
```
/usr/local/etc/postfix/master.cf:
nncp      unix  -       n       n       -       -       pipe
          flags=F user=nncp argv=nncp-exec -quiet $nexthop sendmail $recipient
```
This runs the nncp-exec command to place outgoing mail into the NNCP queue after replacing $nexthop by the the receiving NNCP node and after replacing $recipient by the recipients. The pipe(8) delivery agent executes the nncp-exec command without assistance from the shell, so there are no problems with shell meta characters in command-line parameters.
Specify that mail for example.com, should be delivered via NNCP, to a host named nncp-host:
```
/usr/local/etc/postfix/transport:
    example.com     nncp:nncp-host
    .example.com    nncp:nncp-host
```
See the transport(5) manual page for more details.
Execute the command postmap /etc/postfix/transport whenever you change the transport file.

Enable transport table lookups:

/usr/local/etc/postfix/main.cf:
    transport_maps = hash:$config_directory/transport

Setting up a Postfix LAN to NNCP gateway

Here is how to relay mail from a LAN via NNCP to the Internet.

You need an nncp-exec program that extracts the sender address from mail that arrives via NNCP, and that feeds the mail into the Postfix sendmail command.
Specify that all remote mail must be sent via the nncp mail transport to your NNCP gateway host, say, nncp-gateway:
```
/usr/local/etc/postfix/main.cf:
    relayhost = nncp-gateway
    default_transport = nncp
```
Postfix 2.0 and later also allows the following more succinct form:
```
/usr/local/etc/postfix/main.cf:
    default_transport = nncp:nncp-gateway
```
Define a pipe(8) based message delivery transport for mail delivery via NNCP:
```
/usr/local/etc/postfix/master.cf:
nncp      unix  -       n       n       -       -       pipe
          flags=F user=nncp argv=nncp-exec -quiet $nexthop sendmail $recipient
```
This runs the nncp-exec command to place outgoing mail into the NNCP queue. It substitutes the hostname (nncp-gateway, or whatever you specified) and the recipients before execution of the command. The nncp-exec command is executed without assistance from the shell, so there are no problems with shell meta characters.
Execute the command postfix reload to make the changes effective.