28.9. SMTP Authentication

Written by James Gorham.

Configuring SMTP authentication on the MTA provides a number of benefits. SMTP authentication adds a layer of security to Sendmail, and provides mobile users who switch hosts the ability to use the same MTA without the need to reconfigure their mail client's settings each time.

  1. Install security/cyrus-sasl2 from the Ports Collection. This port supports a number of compile-time options. For the SMTP authentication method demonstrated in this example, make sure that LOGIN is not disabled.

  2. After installing security/cyrus-sasl2, edit /usr/local/lib/sasl2/Sendmail.conf, or create it if it does not exist, and add the following line:

    pwcheck_method: saslauthd
  3. Next, install security/cyrus-sasl2-saslauthd and add the following line to /etc/rc.conf:

    saslauthd_enable="YES"

    Finally, start the saslauthd daemon:

    # service saslauthd start

    This daemon serves as a broker for sendmail to authenticate against the FreeBSD passwd(5) database. This saves the trouble of creating a new set of usernames and passwords for each user that needs to use SMTP authentication, and keeps the login and mail password the same.

  4. Next, edit /etc/make.conf and add the following lines:

    SENDMAIL_CFLAGS=-I/usr/local/include/sasl -DSASL
    SENDMAIL_LDFLAGS=-L/usr/local/lib
    SENDMAIL_LDADD=-lsasl2

    These lines provide Sendmail the proper configuration options for linking to cyrus-sasl2 at compile time. Make sure that cyrus-sasl2 has been installed before recompiling Sendmail.

  5. Recompile Sendmail by executing the following commands:

    # cd /usr/src/lib/libsmutil
    # make cleandir && make obj && make
    # cd /usr/src/lib/libsm
    # make cleandir && make obj && make
    # cd /usr/src/usr.sbin/sendmail
    # make cleandir && make obj && make && make install

    This compile should not have any problems if /usr/src has not changed extensively and the shared libraries it needs are available.

  6. After Sendmail has been compiled and reinstalled, edit /etc/mail/freebsd.mc or the local .mc. Many administrators choose to use the output from hostname(1) as the name of .mc for uniqueness. Add these lines:

    dnl set SASL options
    TRUST_AUTH_MECH(`GSSAPI DIGEST-MD5 CRAM-MD5 LOGIN')dnl
    define(`confAUTH_MECHANISMS', `GSSAPI DIGEST-MD5 CRAM-MD5 LOGIN')dnl

    These options configure the different methods available to Sendmail for authenticating users. To use a method other than pwcheck, refer to the Sendmail documentation.

  7. Finally, run make(1) while in /etc/mail. That will run the new .mc and create a .cf named either freebsd.cf or the name used for the local .mc. Then, run make install restart, which will copy the file to sendmail.cf, and properly restart Sendmail. For more information about this process, refer to /etc/mail/Makefile.

To test the configuration, use a MUA to send a test message. For further investigation, set the LogLevel of Sendmail to 13 and watch /var/log/maillog for any errors.

For more information, refer to SMTP authentication.

All FreeBSD documents are available for download at http://ftp.FreeBSD.org/pub/FreeBSD/doc/

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