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Sendmail-SMTP-AUTH-TLS-Howto

Version 1.0
Author: Falko Timme <ft [at] falkotimme [dot] com>
Last edited 03/11/2004

This document describes how to install a mail server based on sendmail that is capable of SMTP-AUTH and TLS. It should work (maybe with slight changes concerning paths etc.) on all *nix operating systems. I tested it on Debian Woody so far.

This howto is meant as a practical guide; it does not cover the theoretical backgrounds. They are treated in a lot of other documents in the web.

This document comes without warranty of any kind!

1 Get the Sources

We need the following software: openssl, cyrus-sasl2, and sendmail. We will install the software from the /tmp directory.

cd /tmp
wget http://www.openssl.org/source/openssl-0.9.7c.tar.gz
wget –passive-ftp ftp://ftp.andrew.cmu.edu/pub/cyrus-mail/cyrus-sasl-2.1.17.tar.gz
wget –passive-ftp ftp://ftp.sendmail.org/pub/sendmail/sendmail.8.12.11.tar.gz

2 Install Openssl

tar xvfz openssl-0.9.7c.tar.gz
cd openssl-0.9.7c
./config
make
make install
ln -s /usr/local/ssl/bin/openssl /usr/bin/openssl

3 Install Cyrus-sasl2

cd /tmp
tar xvfz cyrus-sasl-2.1.17.tar.gz
cd cyrus-sasl-2.1.17
./configure –enable-anon –enable-plain –enable-login –disable-krb4 –with-saslauthd=/var/run/saslauthd –with-pam –with-openssl=/usr/local/ssl –with-plugindir=/usr/local/lib/sasl2 –enable-cram –enable-digest –enable-otp (1 line!)
make
make install

If /usr/lib/sasl2 exists: 
mv /usr/lib/sasl2 /usr/lib/sasl2_orig

echo “pwcheck_method: saslauthd” > /usr/local/lib/sasl2/Sendmail.conf
echo “mech_list: login plain” >> /usr/local/lib/sasl2/Sendmail.conf

mkdir -p /var/run/saslauthd

4 Create Certificates for TLS

mkdir -p /etc/mail/certs
cd /etc/mail/certs
openssl req -new -x509 -keyout cakey.pem -out cacert.pem -days 365

<- Enter your password for smtpd.key.
<- Enter your Country Name (e.g., “DE”).
<- Enter your State or Province Name.
<- Enter your City.
<- Enter your Organization Name (e.g., the name of your company).
<- Enter your Organizational Unit Name (e.g. “IT Department”).
<- Enter the Fully Qualified Domain Name of the system (e.g. “server1.example.com”).
<- Enter your Email Address.

openssl req -nodes -new -x509 -keyout sendmail.pem -out sendmail.pem -days 365

<- Again, enter your password for smtpd.key.
<- Enter your Country Name (e.g., “DE”).
<- Enter your State or Province Name.
<- Enter your City.
<- Enter your Organization Name (e.g., the name of your company).
<- Enter your Organizational Unit Name (e.g. “IT Department”).
<- Enter the Fully Qualified Domain Name of the system (e.g. “server1.example.com”).
<- Enter your Email Address.

openssl x509 -noout -text -in sendmail.pem
chmod 600 ./sendmail.pem

5 Install Sendmail

cd /tmp
tar xvfz sendmail.8.12.11.tar.gz
cd sendmail-8.12.11/devtools/Site/

Create the file site.config.m4 (in devtools/Site/):

# SASL2 (smtp authentication)
APPENDDEF(`confENVDEF', `-DSASL=2')
APPENDDEF(`conf_sendmail_LIBS', `-lsasl2')
#
# STARTTLS (smtp + tls/ssl)
APPENDDEF(`conf_sendmail_ENVDEF', `-DSTARTTLS')
APPENDDEF(`conf_sendmail_ENVDEF', `-D_FFR_SMTP_SSL')
APPENDDEF(`conf_sendmail_LIBS', `-lssl -lcrypto -L/usr/local/ssl/lib')

 
mkdir -p /usr/man
mkdir -p /usr/man/man1
mkdir -p /usr/man/man8
cp -pfr /usr/local/lib/sasl2 /usr/lib/sasl2
echo /usr/lib/sasl2 >> /etc/ld.so.conf
ldconfig
ln -s /usr/local/ssl/include/openssl /usr/include/openssl

Now we can compile sendmail:

cd /tmp/sendmail-8.12.11/
useradd smmsp
groupadd smmsp
sh Build -c
sh Build install

Let’s create our sendmail.cf:

cd cf/cf/

Create the file sendmail.mc with the following contents:

dnl ### do SMTPAUTH
define(`confAUTH_MECHANISMS', `LOGIN PLAIN DIGEST-MD5 CRAM-MD5')dnl
TRUST_AUTH_MECH(`LOGIN PLAIN DIGEST-MD5 CRAM-MD5')dnl

dnl ### do STARTTLS
define(`confCACERT_PATH', `/etc/mail/certs')dnl
define(`confCACERT', `/etc/mail/certs/cacert.pem')dnl
define(`confSERVER_CERT', `/etc/mail/certs/sendmail.pem')dnl
define(`confSERVER_KEY', `/etc/mail/certs/sendmail.pem')dnl
define(`confCLIENT_CERT', `/etc/mail/certs/sendmail.pem')dnl
define(`confCLIENT_KEY', `/etc/mail/certs/sendmail.pem')dnl
DAEMON_OPTIONS(`Family=inet, Port=465, Name=MTA-SSL, M=s')dnl

dnl ###
define(`confDEF_CHAR_SET', `iso-8859-1')dnl
define(`confMAX_MESSAGE_SIZE', `15000000')dnl Denial of Service Attacks
define(`confMAX_DAEMON_CHILDREN', `30')dnl Denial of Service Attacks
define(`confCONNECTION_RATE_THROTTLE', `2')dnl Denial of Service Attacks
define(`confMAXRCPTSPERMESSAGE', `50')dnl Denial of service Attacks
define(`confSINGLE_LINE_FROM_HEADER', `True')dnl
define(`confSMTP_LOGIN_MSG', `$j')dnl
define(`confDONT_PROBE_INTERFACES', `True')dnl
define(`confTO_INITIAL', `6m')dnl
define(`confTO_CONNECT', `20s')dnl
define(`confTO_HELO', `5m')dnl
define(`confTO_HOSTSTATUS', `2m')dnl
define(`confTO_DATAINIT', `6m')dnl
define(`confTO_DATABLOCK', `35m')dnl
define(`confTO_DATAFINAL', `35m')dnl
define(`confDIAL_DELAY', `20s')dnl
define(`confNO_RCPT_ACTION', `add-apparently-to')dnl
define(`confALIAS_WAIT', `0')dnl
define(`confMAX_HOP', `35')dnl
define(`confQUEUE_LA', `5')dnl
define(`confREFUSE_LA', `12')dnl
define(`confSEPARATE_PROC', `False')dnl
define(`confCON_EXPENSIVE', `true')dnl
define(`confWORK_RECIPIENT_FACTOR', `1000')dnl
define(`confWORK_TIME_FACTOR', `3000')dnl
define(`confQUEUE_SORT_ORDER', `Time')dnl
define(`confPRIVACY_FLAGS', `authwarnings,goaway,restrictmailq,restrictqrun,needmailhelo')dnl
OSTYPE(linux)dnl
FEATURE(`delay_checks')dnl
FEATURE(`generics_entire_domain')dnl
FEATURE(`local_procmail')dnl
FEATURE(`masquerade_envelope')dnl
FEATURE(`nouucp',`reject')dnl
FEATURE(`redirect')dnl
FEATURE(`relay_entire_domain')dnl
FEATURE(`use_cw_file')dnl
FEATURE(`virtuser_entire_domain')dnl

FEATURE(dnsbl,`blackholes.mail-abuse.org',
` Mail from $&{client_addr} rejected; see http://mail-abuse.org/cgi-bin/lookup?$& {client_addr}')dnl
FEATURE(dnsbl,`dialups.mail-abuse.org',
` Mail from dial-up rejected; see http://mail-abuse.org/dul/enduser.htm')dnl

FEATURE(`virtusertable',`hash -o /etc/mail/virtusertable')dnl
FEATURE(access_db)dnl
FEATURE(lookupdotdomain)dnl
FEATURE(`blacklist_recipients')dnl
FEATURE(`no_default_msa')dnl
DAEMON_OPTIONS(`Port=smtp, Name=MTA')dnl
MAILER(local)dnl
MAILER(smtp)dnl
MAILER(procmail)dnl

In order to create /etc/mail/sendmail.cf run the following commands:

sh Build sendmail.cf
cp sendmail.cf /etc/mail/sendmail.cf

Finally we have to create some files:

cd /etc/mail/
touch /etc/mail/local-host-names
touch /etc/mail/virtusertable
/usr/sbin/makemap hash virtusertable < virtusertable
mkdir -p /var/spool/mqueue
chmod 700 /var/spool/mqueue
chown root:root /var/spool/mqueue
chown root:root /etc/mail/sendmail.cf
chmod 444 /etc/mail/sendmail.cf
chown root:root /etc/mail/submit.cf
chmod 444 /etc/mail/submit.cf
touch /etc/mail/aliases
newaliases
touch /etc/mail/access
/usr/sbin/makemap hash access < access

We need an init script for sendmail (this should be copied to /etc/init.d/sendmail):

#! /bin/sh

case "$1" in
    start)
        echo "Initializing SMTP port. (sendmail)"
        /usr/sbin/sendmail -bd -q1h
        ;;
    stop)
        echo "Shutting down SMTP port:"
        killall /usr/sbin/sendmail
        ;;
    restart|reload)
        $0 stop  &&  $0 start
        ;;
    *)
        echo "Usage: $0 {start|stop|restart|reload}"
        exit 1
esac
exit 0

chmod 755 /etc/init.d/sendmail

In order to start sendmail at boot time do the following:

ln -s /etc/init.d/sendmail /etc/rc2.d/S20sendmail
ln -s /etc/init.d/sendmail /etc/rc3.d/S20sendmail
ln -s /etc/init.d/sendmail /etc/rc4.d/S20sendmail
ln -s /etc/init.d/sendmail /etc/rc5.d/S20sendmail
ln -s /etc/init.d/sendmail /etc/rc0.d/K20sendmail
ln -s /etc/init.d/sendmail /etc/rc1.d/K20sendmail
ln -s /etc/init.d/sendmail /etc/rc6.d/K20sendmail

6 Configure Saslauthd

Create /etc/init.d/saslauthd:

#!/bin/sh -e

NAME=saslauthd
DAEMON="/usr/sbin/${NAME}"
DESC="SASL Authentication Daemon"
DEFAULTS=/etc/default/saslauthd

test -f "${DAEMON}" || exit 0

# Source defaults file; edit that file to configure this script.
if [ -e "${DEFAULTS}" ]; then
    . "${DEFAULTS}"
fi

# If we're not to start the daemon, simply exit
if [ "${START}" != "yes" ]; then
    exit 0
fi

# If we have no mechanisms defined
if [ "x${MECHANISMS}" = "x" ]; then
    echo "You need to configure ${DEFAULTS} with mechanisms to be used"
    exit 0
fi

# Add our mechanimsms with the necessary flag
for i in ${MECHANISMS}; do
    PARAMS="${PARAMS} -a ${i}"
done

# Consider our options
case "${1}" in
  start)
        echo -n "Starting ${DESC}: "
        ln -fs /var/spool/postfix/var/run/${NAME} /var/run/${NAME}
        ${DAEMON} ${PARAMS}
        echo "${NAME}."
        ;;
  stop)
        echo -n "Stopping ${DESC}: "
        PROCS=`ps aux | grep -iw '/usr/sbin/saslauthd' | grep -v 'grep' |awk '{print $2}' | tr '\n' ' '`
        if [ "x${PROCS}" != "x" ]; then
          kill -15 ${PROCS} &> /dev/null
        fi
        echo "${NAME}."
        ;;
  restart|force-reload)
        $0 stop
        sleep 1
        $0 start
        echo "${NAME}."
        ;;
  *)
        echo "Usage: /etc/init.d/${NAME} {start|stop|restart|force-reload}" >&2
        exit 1
        ;;
esac

exit 0

 
chmod 755 /etc/init.d/saslauthd

In order to start saslauthd at boot time do the following:

ln -s /etc/init.d/saslauthd /etc/rc2.d/S20saslauthd
ln -s /etc/init.d/saslauthd /etc/rc3.d/S20saslauthd
ln -s /etc/init.d/saslauthd /etc/rc4.d/S20saslauthd
ln -s /etc/init.d/saslauthd /etc/rc5.d/S20saslauthd
ln -s /etc/init.d/saslauthd /etc/rc0.d/K20saslauthd
ln -s /etc/init.d/saslauthd /etc/rc1.d/K20saslauthd
ln -s /etc/init.d/saslauthd /etc/rc6.d/K20saslauthd

Then create /etc/default/saslauthd:

# This needs to be uncommented before saslauthd will be run automatically
START=yes

# You must specify the authentication mechanisms you wish to use.
# This defaults to "pam" for PAM support, but may also include
# "shadow" or "sasldb"
MECHANISMS=shadow

If you find out that saslauthd is located in /usr/local/sbin instead of /usr/sbin create a symbolic link:

ln -s /usr/local/sbin/saslauthd /usr/sbin/saslauthd

Then start saslauthd and sendmail:

/etc/init.d/saslauthd start

/etc/init.d/sendmail start

7 Test your Configuration

To verify that your sendmail was compiled with the right options type

/usr/sbin/sendmail -d0.1 -bv root

You should see that sendmail was compiled with SASLv2 and STARTTLS:

To see if SMTP-AUTH and TLS work properly now run the following command:

telnet localhost 25

After you have established the connection to your sendmail mail server type

ehlo localhost

If you see the lines

250-STARTTLS

and

250-AUTH

everything is fine.

Type

quit

to return to the system’s shell.

Links

Sendmail MTA: http://www.sendmail.org/

OpenSSL: http://www.openssl.org/

Cyrus-SASL: http://asg.web.cmu.edu/sasl/