sendmail: Introduction and Configuration
By Eric Seneca on Thu, 2001-11-29 02:00.HOWTOs
A guide for those of you configuring your first e-mail server.
With the growth of the Internet, e-mail has quickly become the main vehicle to spread information through the public at large. As the demand for fast, cheap and reliable e-mail grows, more individuals are turning to Linux to provide a fast, cheap and reliable solution.
sendmail was originally developed by Eric Allman, in 1979, as "delevermail", which first shipped with BSD 4.0. This program was not very flexible and required configuration at compile time. With the growth of TCP protocol and other factors, it became obvious that delevermail was not flexible enough to handle these new demands. Eric Allman had to recreate sendmail from scratch, and what he produced has become the standard for MTAs. Rather than reject messages that were did not conform to protocols, sendmail is designed to be tolerant of these messages. For those individuals who have never configured an e-mail server, this article will demonstrate how to configure sendmail 8.11.2 after a fresh install of Red Hat Linux 7.1.
By default, sendmail 8.11 is installed during the Red Hat Linux 7.1 installation. As Red Hat has progressed over the years, the installation process has become very easy. Though this article will not go into installation details, further documentation is provided on the Red Hat CD set.
For your new e-mail server to work, you must first get all the DNS issues straight. First, add the hostname and IP address for the new e-mail server to your DNS server and confirm the address with nslookup:
[root@testmail /root]# nslookup -sil testmail.blank.com
Server: 192.168.100.1
Address: 192.168.100.1#53
Name: testmail.blank.com
Address: 192.168.100.134
It is also important that your administrator put a reverse DNS entry to prevent delays in mail delivery. Most modern e-mail servers use reverse lookup as a means of authentication for mail transfer. Again, confirm this setting is correct using the nslookup command on your IP address.
[root@testmail /root]# nslookup -sil 192.168.100.134
Server: 192.168.100.1
Address: 192.168.100.1#53
134.100.168.192.in-addr.arpa name = TESTMAIL.blank.com.
As you can see, the DNS entries are setup and working correctly, so let's move on to actually configuring sendmail. By default, sendmail installations on Red Hat will only allow SMTP traffic on the localhost. The output of netstat -nl will show you all ports that have a dæmon listening; note the line that says 127.0.0.1:25. This means the server is only listening on the loop back interface for connections on port 25 (SMTP).
[root@testmail /root]# netstat -nl
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address
State
tcp 0 0 0.0.0.0:32768 0.0.0.0:*
LISTEN
tcp 0 0 0.0.0.0:111 0.0.0.0:*
LISTEN
tcp 0 0 0.0.0.0:22 0.0.0.0:*
LISTEN
tcp 0 0 127.0.0.1:25 0.0.0.0:*
LISTEN
udp 0 0 0.0.0.0:32768 0.0.0.0:*
udp 0 0 0.0.0.0:667 0.0.0.0:*
udp 0 0 0.0.0.0:111 0.0.0.0:*
Active UNIX domain sockets (only servers)
Proto RefCnt Flags Type State I-Node Path
unix 2 [ ACC ] STREAM LISTENING 1119 /dev/gpmctl
unix 2 [ ACC ] STREAM LISTENING 1172
/tmp/.font-unix/fs7100
This will keep your mail dæmon from accepting e-mail from any computer except the localhost. To fix this issue, we must tell sendmail to listen for connections on the external interface. In the case of our new server, there is only one Ethernet card, with eth0 being the external interface. To confirm the IP on eth0, simply perform an ifconfig. Depending on your configuration, this IP can be different than the address defined by your DNS server, but in our example the addresses are the same.
[root@testmail /root]# ifconfig
eth0 Link encap:Ethernet HWaddr 00:60:97:DE:E9:99
inet addr:192.168.100.134 Bcast:192.168.100.255
Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:12421 errors:0 dropped:0 overruns:0 frame:0
TX packets:5 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:100
Interrupt:10 Base address:0xe000
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:6 errors:0 dropped:0 overruns:0 frame:0
TX packets:6 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
This machine has an address of 192.168.100.134 on the eth0 interface. Once you have that address, edit the /etc/sendmail.cf file and configure the sendmail dæmon to listen on the address.
# SMTP daemon options
O DaemonPortOptions=Port=smtp,Addr=127.0.0.1, Name=MTA
change to
O DaemonPortOptions=Port=smtp,Addr=192.168.100.134, Name=MTA
Once you have completed this task, save this file and restart the sendmail dæmon using the rc script /etc/init.d/sendmail.
[root@testmail /root]# /etc/init.d/sendmail restart
Shutting down sendmail: [ OK ]
Starting sendmail: [ OK ]
[root@testmail /root]#
Now check to see if there has been a change with the netstat -nl command. As you can see the output clearly shows that a dæmon (sendmail) is listening on port 25 of the IP address 192.168.100.134 that is assigned to our interface eth0.
[root@testmail /root]# netstat -nl
Active Internet connections (only servers)
Proto Recv-Q send-Q Local Address Foreign Address
State
tcp 0 0 0.0.0.0:32768 0.0.0.0:*
LISTEN
tcp 0 0 0.0.0.0:111 0.0.0.0:*
LISTEN
tcp 0 0 0.0.0.0:22 0.0.0.0:*
LISTEN
tcp 0 0 192.168.100.134:25 0.0.0.0:*
LISTEN
udp 0 0 0.0.0.0:32768 0.0.0.0:*
udp 0 0 0.0.0.0:667 0.0.0.0:*
udp 0 0 0.0.0.0:111 0.0.0.0:*
Active UNIX domain sockets (only servers)
Proto RefCnt Flags Type State I-Node Path
unix 2 [ ACC ] STREAM LISTENING 1119 /dev/gpmctl
unix 2 [ ACC ] STREAM LISTENING 1172
/tmp/.font-unix/fs7100
[root@testmail /root]#
Now that we have sendmail accepting external connections, we need to assign the domains that can be accepted. This can be accomplished with the /etc/mail/local-host-names file. Simply put the domain name, blank.com, in the file.
# local-host-names - include all aliases for your machine here.
blank.com
Once this information is saved in this file, restart the sendmail dæmon with the rc script sendmail found in /etc/init.d/sendmail restart. sendmail can accept e-mail for multiple domains on the same server. Insert the domain name into this file each time you want to add a new domain.
You now have a fully working e-mail server from the localhost. It can accept e-mail from anywhere in the world, but can only send e-mail or relay e-mail from the localhost. Another default security feature is that sendmail will not allow the relay of any mail to prevent spam originating from your server. If your users log directly into the server, this configuration does not need modification. But if your organization is like most, clients are using e-mail from remote sites. If your users use clients like KMail or Outlook Express, you will need to allow those machines to relay e-mail using your new server, but you do not want to open your site up to complete relay. This can be done by adding the following line to the /etc/mail/access file and running the command make access.db after saving that file.
blank.com RELAY
# Check the /usr/share/doc/sendmail-8.11.2/README.cf file for a
description
# of the format of this file. (search for access_db in that file)
# The /usr/share/doc/sendmail-8.11.2/README.cf is part of the
sendmail-doc
# package.
#
# by default we allow relaying from localhost...
localhost.localdomain RELAY
localhost RELAY
127.0.0.1 RELAY
blank.com RELAY
[root@testmail mail]# make access.db
[root@testmail mail]#
The make access.db command will include your new setting in the hash database used by sendmail to determine who can relay e-mail off your server. This will allow connections from inside the blank.com domain to relay e-mail from your new mail server, and prevent use of the service to nonmembers. One can also put a subnet of IPs, such as 192.168, to limit inside a domain. Keep in mind that if this setting is to open, spammers can bounce huge amounts of e-mail off your system.
Now that you can accept e-mail from anywhere in the world, have configured your domain, and allowed relay e-mail for approved clients, you may want to allow remote access to that mail. This can be accomplished with IMAP or POP. With a default server install, not all required packages are installed to make POP/IMAP mail work. These services can be obtained by the installation of the imap-2000-9 rpm package. To check the install status of this package use the following command: rpm -aq | grep -i imap. If no package is found, insert Disk 2 of the Red Hat 7.1 installation disk set into your cd-rom and mount that media. To accomplish this use the mount /dev/cdrom /mnt/cdrom command.
[root@testmail mail]# mount /dev/cdrom /mnt/cdrom
mount: block device /dev/cdrom is write-protected, mounting read-only
(Successful Mount of Read-Only Media)
Once mounted you can install the package with rpm -Uvh
/mnt/cdrom/RedHat/RPMS/imap-2000-9.i386.rpm.
[root@testmail mail]# rpm -Uvh
/mnt/cdrom/RedHat/RPMS/imap-2000-9.i386.rpm
Preparing... ###########################################
[100%]
1:imap ###########################################
[100%]
As you can see, when I run the rpm search, rpm -aq | grep -i
imap the IMAP package is displayed with output.
[root@testmail mail]# rpm -aq | grep -i imap
imap-2000-9
[root@testmail mail]#
With the correct package install, you now need to enable POP3 connections to your new e-mail server. This can be accomplished in the /etc/xinetd.d directory by modifying the ipop3 file. Set the value for disable to no, and save the file. Remember to maintain the case as it appears in the file.
# default: off
# description: The POP3 service allows remote users to access their mail
\
# using an POP3 client such as Netscape Communicator, mutt,
\
# or fetchmail.
service pop3
{
socket_type = stream
wait = no
user = root
server = /usr/sbin/ipop3d
log_on_success += USERID
log_on_failure += USERID
disable = no
}
Now you need to restart the xinetd dæmon to make the new setting work. This is possible by using the rc script /etc/init.d/xinetd. Simply issue the restart command as seen below.
[root@testmail xinetd.d]# /etc/init.d/xinetd restart
Stopping xinetd: [ OK ]
Starting xinetd: [ OK ]
[root@testmail xinetd.d]#
Now send a test e-mail to your new server and connect to the server via your favorite pop client. You should now be able to access your e-mail via POP protocol.
One final consideration about your new server is performance. You may receive complaints about slow connection to your POP server if the client traffic is being initiated from behind a firewall. The reason for this delay is that your e-mail server initiates a IDENT session with the client to confirm the identity of the client. If there is no response to that query, the server will invoke a timeout value set by default to 5 seconds. This value can be reduced to 1 second to remove most of the delay caused by IDENT. To change this value edit the /etc/sendmail.cf file, and reduce the timeout value to the desired value.
# timeouts (many of these)
#O Timeout.ident=5s
change to
O Timeout.ident=1s
Your e-mail server is now working and providing service to your users. There are many more configurations for sendmail that are beyond the scope of this article. Linux will provide a very stable, robust platform for your e-mail needs. To find more information about sendmail visit .
Eric Jorn Seneca is a UNIX system engineer in Baton Rouge, Louisiana.
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Thanks So Much
Submitted by Adam Doupe (not verified) on Wed, 2006-08-30 14:07.
Hey, I really appreciate this article, it helped me set up sendmail quickly. Thanks for the good article.
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Problem with spams
Submitted by parikshit (not verified) on Fri, 2006-08-18 04:42.
Hi,
I am developing an application in jsp. we are using java mail api to send email through our application.
The problem with us is that our mais are landing in spam folders in a few public domain email providers.
One of the spam lists says that our mail server is not correctly configured and thats why our mails are landing in spam folder.
here is the link:
thanks in advance.
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creating user accounts after configuring sendmail
Submitted by Den (not verified) on Tue, 2006-05-23 07:24.
Hi,
I do appreciate for your nice material on configuring sendmail.I have successfully managed to follow it the end but question is how do i create email accounts for users in my email server
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Excellent job
Submitted by Anonymous (not verified) on Thu, 2006-04-20 02:11.
Excellent job ...... Thanks a lot
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thanks Eric!
Submitted by Vitu (not verified) on Thu, 2006-01-05 08:39.
Thanks Eric, this article is great.
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Please explain some more
Submitted by Sreedhar.T.P (not verified) on Sun, 2006-03-19 03:19.
I saw ur article and found it intersting. Iam new to Linux and i have a handful of doubts. Will u please explain me...
By configuring sendmail can i add unlimited users
Where will be the email data stored
Will this configuration work in Red Hat Enterprise Linux AS4
Can i configure it it GUI mode.
Is it easy to administer
Expecting a detailed reply
Thanking you
Sreedhar
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sendmail config
Submitted by JaR (not verified) on Tue, 2005-09-06 01:32.
need some help
i have a smtp working with pop3 runing
my problem is some ips use my server for spam
how i can stop that?
tcp 0 0 nicolaescumalex.pi:smtp 221.221.234.210:2865 ESTABLISHED
tcp 0 0 nicolaescumalex.pi:smtp 221.221.234.227:2658 ESTABLISHED
tcp 0 0 nicolaescumalex.pi:smtp 221.221.255.137:bmap ESTABLISHED
tcp 0 0 nicolaescumalex.pi:smtp 221.221.255.94:2725 ESTABLISHED
tcp 0 0 nicolaescumalex.pi:smtp 221.221.255.94:4754 ESTABLISHED
tcp 0 0 nicolaescumalex.pi:smtp 221.221.232.215:2402 ESTABLISHED
tcp 0 0 nicolaescumalex.pi:smtp 221.221.255.137:4755 ESTABLISHED
this are the conection to my smtp
they are using big list of email address and have wrong addres in the list
i receive mails like this
From: Mail Delivery Subsystem
Subject: Postmaster notify: see transcript for details
This is a MIME-encapsulated message
--j867TerR011920.1125991785/nicolaescumalex.piatraneamt.rdsnet.ro
The original message was received at Tue, 6 Sep 2005 07:29:40 GMT
my question is
how they can access my smtp and how i can blok it??
thx
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prevent spammers from using my sendmail
Submitted by Anonymous (not verified) on Thu, 2006-02-16 10:53.
Has anyone responded to this posting?
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Hi, Is it possible to read m
Submitted by jibu (not verified) on Fri, 2005-09-02 05:20.
Hi,
Is it possible to read messages directly from sendmail using java without using pop3?
Thanks
Jibu
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Re: Sendmail Configuration.
Submitted by Abbass (not verified) on Fri, 2005-08-12 04:32.
This article is really great.
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Can't recieve mail externaly or localy
Submitted by CharlesB (not verified) on Sun, 2005-11-06 16:57.
I am relitivly new to linux "mandrake 10.0" I have read your step by step on setting up sendmail..... "Perfect simple absolutly the best I have read". I can send emails externaly and localy but for the life of me I can not recieve mails sent to the mail server here. I have tryed everything I could think of and have read "including your step by step". Nothing seems to be working at all for me :(
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Relaying help needed
Submitted by Andre (not verified) on Fri, 2004-11-26 05:56.
I have a fully working sendmail set up going, I can send mail using a web client (Squirrelmail) and receive mail fine using a POP3 server and IMAP. I cannot send mail from home using a client like Outlook, I get "RELAY DENIED" error, but I can download my mail from the server.
I've tried auth settings on the client side, but nothing seems to work when I send mail to a domain not listed in my relay-domains list. Obviously I can't add all domains or *.com etc, as that will open the relay. Any ideas/comments/suggestions?!
I need to get this working, without using the ISP's SMTP server for sending, I've got a client that wants to use this server in house...
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Re: Relaying Help needed
Submitted by Rohit (not verified) on Fri, 2006-03-24 09:36.
Hi,
I am also facing the same problem as you, If you have found some solutions for the same, then pls share with me..
Thanks
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It feels good to see smtp working....
Submitted by Chris Jackson (not verified) on Wed, 2004-11-24 22:19.
I have tried and tried to get sendmail working - awesome article. Thanks...
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problem in accessinig access file
Submitted by mks (not verified) on Mon, 2004-11-15 23:52.
Hi,
I have read the following line in ur article for configuring sendmail.
This can be done by adding the following line to the /etc/mail/access file and running the command make access.db after saving that file.
blank.com RELAY
But when i tried to access /etc/mail/access file, it is asking for encryption key. What should i do now?
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Re: sendmail: Introduction and Configuration
Submitted by Anonymous on Sun, 2004-06-20 01:00.
Erick,
YOU ARE THE CHAMPION MY FRIEND.
Miguel
Miami, FL
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Re: sendmail: Introduction and Configuration
Submitted by Anonymous on Tue, 2004-04-20 01:00.
Very good article because it's simple and complete. It worked fine. The only thing would be to explain thant this pop3 works on port 995
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Re: sendmail: Introduction and Configuration
Submitted by Anonymous on Mon, 2003-11-17 02:00.
Good Job Eric. Good combination of stuff put together. Good for new linux net admins.
Thanks on every ones behalf