Transport can do a lot of things. Here's an example.
In main.cf, you have the entry
Code:
transport_maps = hash:/etc/postfix/transport
or similar.
Now in my transport file, I have entries like:
Code:
fax.mydomain.com fax:localhost
fax_ps.mydomain.com fax_ps:localhost
In master.cf
Code:
fax unix - n n - 1 pipe
flags= user=fax argv=/usr/local/bin/faxmail -d -n ${user}
fax_ps unix - n n - 1 pipe
flags= user=fax argv=/etc/postfix/fax_ps -u ${user}
When a message is sent to
user@fax.mydomain.com, the fax transport agent is called with the user (in this case the fax num,ber) as a parameter (fax_ps faxes a postscript file, the basic version faxes the mail body)
Hope that makes some sense.