As part of my scheme to setup the Debian machine, chrome, as the
backup for the mail/web server, I had to grapple with exim, the MTA
offered as default by Debian. This appeared a little simpler to
configure than sendmail. To make exim run in the same manner as
sendmail on crimson, the following configuration options were set
(among many standard settings) in /etc/exim/exim.conf:
# MAIN configuration qualify_domain = hydrus.org.uk local_domains = hydrus.org.uk:localhost # ROUTER Configuration smarthost: driver = domainlist transport = remote_smtp route_list = "* smtp.isp.com bydns_a"
These settings ensure that sender mail addresses were set as
user@hydrus.org.uk and that my ISP's mail server was used
to send all outgoing messages. You must also ensure that the fully
qualified machine name is placed into /etc/hosts, either
against 127.0.0.1 for machines where the IP is assigned via DHCP, or
against the static IP assigned. The FQDN must be the first name
specified. If this is not done, exim will refuse to accept mail for
the machine, claiming it is being used as a relay.
At this point I thought about investigating whether I could persuade
exim to handle the sending of mail to other machines in the domain.
I had tried something similar before (see The Sendmail Saga), with only
limited success. If the envelope was set to
user@hydrus.org.uk, for mail sent to say, crimson, then the
mail would (a) be rejected because the Alcatel router denied a
domain of hydrus.org.uk existed, and (b) it would be impossible to
reply to the mail as the information about the originating machine
was not present. Setting the default qualify_domain to
chrome.hydrus.org.uk will not work, as it is not possible
to send mail outside of the domain, since the ISP's mail server will
fail to find any DNS entries for chrome, and bounce the mail.
After a little experimentation, I found the following additions to the exim configuration file had the desired effect:
# First, define a transport for local machines. This performs
# rewriting of the envelope (return_path) and headers to
# indicate the mail is from chrome.
local_smtp:
driver = smtp
return_path = ${local_part}@chrome.hydrus.org.uk
headers_rewrite = *@hydrus.org.uk ${1}@chrome.hydrus.org.uk fr
# In the ROUTES section, a new router is defined, which handles
# recipient addresses on domain machines - anything ending in
# the domain name, and unadorned host names (assuming they
# contain no digits). If the recipient does not match anything
# in the domains value the smarthost router is used.
local_network:
driver = lookuphost
transport = local_smtp
domains = *.hydrus.org.uk:^[A-Za-z]*\$
This setup ensured that when mail was sent to a machine within the hydrus domain, the addresses were re-written to add chrome. The fully qualified machine name meant that the sendmail DNS lookups on the Alcatel router would return local IP addresses. Now, was it possible to get sendmail to handle things the same way?
I discovered later that a solution to this problem is in the Exim FAQ.
