Computing Service staff develop and maintain Exim, which runs on Hermes and ppswitch. Mail Support are therefore able to offer expert help with it, and we recommend that if you need to run an MTA on a Unix machine on the Cambridge University Data Network, you should use Exim. We have a suggested configuration file which is designed to do the right thing according to the rules for the use of email within the University, and we are happy to provide advice on how to adjust this configuration for your particular case.
However, many Linux and Unix distributions now come with Postfix as the standard MTA. We have limited experience with it though we try to offer advice when we can. If you do not want to install Exim, this document describes how to configure Postfix so that it will emit correctly-addressed email that will be accepted by ppswitch.
The first thing to do is to configure Postfix to send all email via
ppsw.cam.ac.uk. Edit the
main.cf file, which
is probably in the directory
/etc/postfix/. You need to
relayhost parameter as follows. Note that the
square brackets are necessary to avoid MX lookups.
relayhost = [ppsw.cam.ac.uk]
By default, Postfix uses the local machine name as its email domain, but computer names within cam.ac.uk are not a valid mail domains according to our rules.
Therefore we must configure Postfix to do some address rewriting,
for which we can use its canonicalization feature. To turn it on, edit
main.cf file to set the
parameter, for example:
canonical_maps = hash:/etc/postfix/canonical
You then need to create the
table. Each line in the file is an email address pattern to match
followed by a replacement address. You want to map all of the
machine's local addresses to an externally valid email address, such
as the address of the machine's admin or the role address of the
responsible group, for example
You probably also want to map some local user addresses to the
The first requirement can be handled with a canonical table entry like
The second requirement wants table entries like this. (The pattern assumes @machine.botolph.cam.ac.uk on the end.)
/etc/postfix/canonical you must run the
postmap /etc/postfix/canonical in order to build
the working lookup table from the text file source. Do this each time
you edit the file.
Finally you must run the command
postfix reload to
update the running configuration with the changes you have made.
Note: we are using the canonical map feature instead of the
"masquerade" feature because the latter would cause email to
email@example.com to go to
The above technique will result in no local delivery of email
(since local addresses are mapped to remote addresses). If you want
local addresses to stay local, you can instead use the "generic
map" for outgoing email. This is exactly the same as using the
canonical map, except the setting to use in
smtp_generic_maps = hash:/etc/postfix/generic
and the file containing the table has a different name. This requires version 2.2 of Postfix, so you should check that your copy is sufficiently new if you choose this route.
$Cambridge: hermes/doc/misc/postfix.html,v 1.6 2008/09/03 12:59:13 fanf2 Exp $