|
| Thursday, June 25, 2009 |
| SENDMAIL configuration |
SENDMAIL Configuration tested on RedHat 4 update 5
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Follow the below link:
http://www.owlriver.com/tips/sendmail-tip/
1> Apply the patch sendmail-cf-8.13.1-3.2.el4.i386.rpm which is available in 3rd cd
rpm -Uvh sendmail-cf-8.13.1-3.2.el4.i386.rpm
2> To be able to hand email TO it (on port 25), you will need packages:
rpm -q sendmail-cf m4
3> If not present, use your install media and install them
4> Edit /etc/mail/sendmail.mc with your favorite text editor. Toward the bottom of that
file is this stanza:
dnl This changes sendmail to only listen on the loopback device 127.0.0.1
dnl and not on any other network devices. Comment this out if you want
dnl to accept email over the network.
DAEMON_OPTIONS(`Port=smtp,Addr=127.0.0.1, Name=MTA')
... Note that the string "dnl " at the left margin is how comments are added to
sendmail.mc -- this is an artifact of the ancient origins of sendmail and the m4 macro
processor
Make it read as the text says "to accept email over the network":
dnl DAEMON_OPTIONS(`Port=smtp,Addr=127.0.0.1, Name=MTA')
(this is the last line quoted in the first stanza, now commented out.)
4. rebuild /etc/sendmail.cf from the revised /etc/mail/sendmail.mc thus:
m4 /etc/mail/sendmail.mc > /etc/sendmail.cf
(This is considered Unix deep magic -- but all it does is have the m4 macro processor use
the sendmail-cf recipies, and make a new well-formed sendmail.cf. Note that lower in the
sendmail.mc file is an option to specify what hostname your mail server uses -- useful for
pretending to be a server with a resolvable name.)
(Note also that /etc/sendmail.cf moves to become /etc/mail/sendmail.cf with sendmail-
8.12.x and so that command will become m4 /etc/mail/sendmail.mc >
/etc/mail/sendmail.cf in later versions. But there are many other changes, including a
separate non-privleged child process.)
5. Tell sendmail to listen all the time (in so-called daemon mode) instead of delivering
just its own local mail queue just once an hour.
Edit /etc/sysconfig/sendmail
and change:
DAEMON=no
to:
DAEMON=yes
6. And restart sendmail
cd /etc/mail
make
service sendmail restart
(Note: The make step is needed in some variants of Red Hat, as the automatic execution
of the make is missing in some releases of the initscript package.)
7. Confirm it locally:
netstat -an | grep 25 | grep tcp
yields:
tcp 0 0 0.0.0.0:25 0.0.0.0:* LISTEN
(which says the host is listening on ALL interfaces for connections ...)
[I undid step 5 and 6 -- and reran this test -- it yields -- nothing -- that it is NOT able to be
connected to externally on port 25 -- and so THAT port is safe from a remote direct
attack.]
8. Test locally (I list YOUR part OUT of []):
telnet localhost 25
[... banner]
HELO LOCALHOST
[... response]
QUIT
It went:
[root@couch herrold]# telnet localhost 25
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
220 couch.basement.net ESMTP Sendmail 8.11.6/8.11.6; Sat, 17
Nov 2001 17:10:39 -0500
HELO localhost
250 couch.basement.net Hello
IDENT:+yf0DRAJjMc1ZxKCEIv/Y7hCZQtbC55G@couch.basement.net
[127.0.0.1], pleased to meet you
QUIT
221 2.0.0 couch.basement.net closing connection
Connection closed by foreign host.
$
9. The acid test -- From another host test it (we'll restate the conversation, and hide the
remote end's responses initially for clarity):
telnet couch.basement.net 25
HELO localhost
QUIT
Or more elaborately (I highlight your input in red):
[herrold@router herrold]$ telnet couch.basement.net 25
Trying 172.16.33.101...
Connected to 172.16.33.101.
Escape character is '^]'.
220 couch.basement.net ESMTP Sendmail 8.11.6/8.11.6; Sat, 17
Nov 2001 17:36:05 -0500
HELO localhost
250 couch.basement.net Hello router.basement.net
[172.16.33.2], pleased to meet you
MAIL FROM:
553 5.5.4 godzilla@localhost... Real domain name required for sender address
MAIL FROM:
250 2.1.0 godzilla@microsoft.com... Sender ok
RCPT TO:
250 2.1.5 root@localhost... Recipient ok
DATA
354 Enter mail, end with "." on a line by itself
Linux rules.
.
250 2.0.0 fAHMajY07056 Message accepted for delivery
QUIT
221 2.0.0 couch.basement.net closing connection
Connection closed by foreign host.
[herrold@router herrold]$
.... that was successful -- note that the 'domain must resolve' rule for senders kicked in on
the first part of the "MAIL FROM" offer -- this is an anti-spam feature. [Note the name
look up's working -- I have working residence DHCP and DNS services on Linux ... ].
The X- header is added by procmail.
There is a forward rule in place for root, as recommended in an earlier post; Out at the
end recipient host, we find:
Return-Path:
Received: from couch.basement.net
(dhcp065-024-xx-xx.columbus.rr.com [65.24.xx.xx])
by swampfox.owlriver.com (8.11.6/8.11.6) with ESMTP id
fAHMbGu07271 for ; Sat, 17 Nov
2001 17:37:16 -0500
Received: from localhost (router.basement.net [172.16.33.2])
by couch.basement.net (8.11.6/8.11.6) with SMTP id
fAHMajY07056
for root@localhost; Sat, 17 Nov 2001 17:37:06 -0500
Date: Sat, 17 Nov 2001 17:37:06 -0500
From: godzilla@microsoft.com
Message-Id: <200111172237.fAHMajY07056@couch.basement.net>
X-Loop: herrold@owlriver.com
Linux rules.
Read the received lines from the bottom up --
We forged the sender as "godzilla@microsoft.com" -- spammers do this all the time,
nothing new there; and offered to root@localhost -- The forward rule handed it for
delivery to herrold@owlriver.com. Seems to work fine
As this demonstrated, this is probably not enough to suffice in production. Do NOT
connect this to the outside world -- a bit more needs to be done --- As set, it will receive
mail only with a final (as to the originator's perspective) destination at the localhost --
/etc/mail/access and /etc/mail/local-host-names need attention to receive mail for
handling for others. But again, this is beyond the scope of this presentation.
10> To send a mail
sendmail –v sriasan@gmail.com – use gmail, I had spam issues with yahoo.com
this is to test sendmail
ctrl –d or .
check gmail for the mailLabels: SENDMAIL configuration |
posted by Srinivasan .R @ 6:03 AM  |
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