Sendmail Configuration Guidence
In this section we will focus on MTAs, I will show you the default implementation, and how to alter the default redhat enterprise implementation
Below packages are required for sendmail configuration
You can check by typing below command:
# rpm -qa | grep sendmail
sendmail-8.13.1-2
# rpm -qa | grep postfix
postfix-2.1.5-4.2.RHEL4
# rpm -ql sendmail
- /etc/mail/access
Can be used to deny access for relaying or receving messages based on the content of the messages
- /etc/mail/acesss.db
Sendmail queries the database version of the file such as berkeley DB
Berkeley DB should be installed to support sendmail to read the DB files.
# file /etc/mail/access*
# rpm -qa | grep -i db
Package Version/Name: db4-4.2.
/etc/mail/helpfile
SMTP commands
e.g. telnet localhost 25
HELP
- /etc/mail/local-host-names
To know how to handle the domains which are considered to be local So it handles routing for
- localhost
- localhost.domain
- FQDN, in my case
- postfix.mydomain.com
- 192.168.10.30
- 127.0.0.1
Default MTA accepts messages for all the above
- /var/spool/mail/
Above directory contains mailbox per user
e.g. /var/spool/mail/~username
Traditional Unix Mbox
Sendmail uses macrotize language called m4, As sendmail configuration is so complex its abstracted to macro utility using m4 -
- /etc/mail/sendmail.mc
1. Just open the sendmail.mc file in VI editor
Search for “/127.0.0.1”
Note : ( If you are configuring as a localhost its applicable Other wise you need to change the IP address as per you need.)
2. Put “dnl” keyword front of the same line.
3. Save the file
4. Fire the below command to sunc the changes from sendmail.mc to sendmail.cf
#pwd
/etc/mail/
#m4 sendmail.mc > sendmail.cf
Restart the sendmail service :
/etc/init.d/sendmail restart
sendmail to user pia
#mail - "test mail" pia@mydomain.comhi,
This test mail.CC:You can check the mail log #tail -f /var/log/maillog | grep "pia@mydomain.com"You can make changes and configure in sendmail.mc Sendmail.mc is much easier to understand
- /etc/mail/sendmail.cf
Sendmails main configuration file
dnl --> way of commenting Sendmail is separated into two daemons:
# ps -ax | grep -i sendmail
- Once accepts connection
e.g. sendmail: accepting connections on port 25
- Other runs the queue
e.g. sendmail: Queue runner@01:00:00 for
/var/spool/clientmqueue
01:00 --> 1 minute
Mails get stored in /var/spool/clientmqueue,
queue runner daemon wakes up every 1 minute
/var/spool/clientmqueue own by smmsp smmsp --> sendmail
mail submission program
So users in our localsystem invokes the mail in local queue /var/spool/clientmqueue, which gets scanned every 1 minute by the queue runner
- /etc/mail/trusted-users
users that can send mail as others without a warning Able to rewrite from section without sendmail complaining
- /etc/mail/virtusertable
Allows us to setup virtual domains e.g. pia@postfix.mydomain.com
pia (local account) So we have given you a brief introduction to the default implementation of sendmail within Redhat framework
Before we migrate to postfix, lets just generate a message and sendmail deliver the mail to the user pia
# which mutt
Mutt is a great client and default it reads mbox format but also have the ability to interact with Maildirs which is newer and more robust way of storing mail messages. However there is any environment variable set which mutt relies upon
# set | grep -i mutt MAIL=/var/spool/mail/root
This environment variable should point to proper users mail box As root you can read anyone's mailbox
# which sendmail
# ls -l /usr/sbin/sendmail
# ls -l /etc/alternatives/mta
SENDMAIL is monolithic. It handles all messaging binding to the MTA port as well as local delivery
# ps -ef | grep sendmail
You could see various instances (process) but all are tied with same binary By default sendmail accepts mails from local user and deliver it to local and remote user
