Sendmail Configuration for Linux (Fedora 11)

This is very similar to the Solaris configuration but the supplied .mc file for linux has rather more FEATURE lines and configuration to start with. The first step is to allow a linux system connected to the internet to send and receive email and to rewrite the addresses as user@domainname

There are two parts to this, one is sendmail configuration and the second is DNS configuration.

Sendmail configuration

First of all we need to create a custom sendmail config file. it is not necessary to edit sendmail.cf files directly, its much easier to generate them from the m4 macro files.

The m4 files on Fedora 11 can be found in /etc/mail/

The standard server sendmail m4 file is called sendmail.mc. Make a copy of the original file so it is easy to backout the changes

First find the line that restricts the sendmail process to only listen on its loopback interface, this is the DAEMON_OPTIONS line which mentions 127.0.0.1. Then comment it out.

Change:

DAEMON_OPTIONS(`Port=smtp,Addr=127.0.0.1, Name=MTA')dnl

to:

dnl # DAEMON_OPTIONS(`Port=smtp,Addr=127.0.0.1, Name=MTA')dnl

Next set the MASQUERADE options to rewrite the outgoing address


MASQUERADE_AS(`mydomain.com')dnl
dnl # masquerade not just the headers, but the envelope as we
dnl #
FEATURE(masquerade_envelope)dnl
dnl #
dnl # masquerade not just @mydomainalias.com, but @*.mydomain
dnl #
FEATURE(masquerade_entire_domain)dnl
dnl #
dnl MASQUERADE_DOMAIN(mydomain.com)dnl

The MASQUERADE_AS line makes all email appear to come from the domain not from the hostname of the system.

#cd /etc/mail
#make

This will produce a new sendmail.cf file
Edit /etc/mail/local-host-names to add the domains that you want to allow relaying for

#vi /etc/mail/local-host-names
mydomain.com
myotherdomain.com

Then restart Sendmail.

service sendmail stop 
service sendmail start

DNS configuration

Add the required MX records to the DNS zone file(s) for your domain(s) similar to the examples below:

mydomain.com		IN	MX	10	mymailserver.mydomain.com
myotherdomain.com	IN	MX	10	mymailserver.mydomain.com

Done ! - Your system should now accept and send email and rewrite outgoing addresses as user@domainname

Using Genericstable feature for rewriting outgoing mail addresses

The generics table can be used to rewrite outgoing mail with more specific requirements for different domains. It allows mail from different users to appear to come from different domains. Add the following to the sendmail m4 file

FEATURE (`genericstable') 
GENERICS_DOMAIN_FILE (`/etc/mail/generics-domains')

The genericstable FEATURE should be added near the end of the file just before the mailer options. If it is added near the beginning of the file the names will not be rewritten correctly.

Run make to make the new custom sendmail config file.

#cd /etc/mail
#make

Edit /etc/mail/generics-domains to add the domain name that gets set by default, typically the hostname

eg,


myhost.mydomain.com

Edit /etc/mail/genericstable to add the users that you want to rewrite outgoing mail for
eg


fred fred@mydomain.com
tom tom_jones@hisdomain.com
bill billybob@myotherdomain.com

Now we need to make the generics table into a map. There are different formats like hash dbm etc. These can be seen by typing 'makemap -l'. The default is type hash which will produce a .db file.

# makemap hash /etc/mail/genericstable < /etc/mail/genericstable

Then restart Sendmail.


service sendmail stop 
service sendmail start

Allowing Relaying with sendmail

If you want to use send email from a wintel client eg. outlook, you will need to setup the server to accept email relays from this client.

This requires the access_db FEATURE in the sendmail m4 file. In Fedora 11 this is normally configured by default so it should not be necessary to add this

FEATURE(`access_db')dnl

Note the extra FEATURE line to enable the access_db feature.

Run make to make the new custom sendmail config file

#cd /etc/mail
#make

Edit /etc/mail/access to add the hosts that you want to allow relaying for
eg.

vi /etc/mail/access
1.2.3.4 RELAY

Now we need to make the access table into a map. There are different formats like hash dbm etc. These can be seen by typing 'makemap -l'. The default is type hash which will produce a .db file.

# makemap hash /etc/mail/access < /etc/mail/access

Then restart Sendmail.

service sendmail stop 
service sendmail start