SENDMAIL Configuration for Comcast Cable and LunarPages

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I have some Linux hosts in my network at home that want to send system messages using SENDMAIL and SMTP. Neither LunarPages nor Comcast have open relays that supports this. Configuring sendmail masquerading will allow these systems to send mail via the LunarPages' or Comcast's SMTP server.

Both LunarPages and Comcast require that the MAIL FROM: address specified during the SMTP dialog match the From: header that’s part of the message data. They also require that the sending e-mail address exist. I changed the default mail routing in my ISP's settings for daveking.com to “:blackhole:” instead of “:fail:” so that any and all e-mail address would be accepted for that domain.

I turned on masquerading in /etc/mail/sendmail.mc. By default, masquerading is disabled for the root user. To enable masquerading for root I commented out the EXPOSED_USER statement in sendmail.mc.

Both Comcast and LunarPages have blocked SMTP port 25 and require the use of SUBMISSION port 587. So far, Lunarpages does not require authentication in oder to use port 587. Comcast does.

The lines I changed in /etc/sendmail.mc are marked with “>>” below. The listing below shows a Lunarpages configuration with the two lines you'd have to change to use Comcast instead commented out.

In addition to modifying /etc/mail/sendmail.mc as shown below, if you're using Comcast, then you'll also have to create a the file called /etc/mail/authinfo that referenced by /etc/mail/sendmail.mc. This file contains your Comcast userid and password. See the comments below for details on that file.

    divert(-1)dnl
    dnl #
    dnl # This is the sendmail macro config file for m4. If you make changes to
    dnl # /etc/mail/sendmail.mc, you will need to regenerate the
    dnl # /etc/mail/sendmail.cf file by confirming that the sendmail-cf package is
    dnl # installed and then performing a
    dnl #
    dnl #     make -C /etc/mail
    dnl #
    include(`/usr/share/sendmail-cf/m4/cf.m4')dnl
    VERSIONID(`setup for Red Hat Linux')dnl
    OSTYPE(`linux')dnl
    dnl #
    dnl # default logging level is 9, you might want to set it higher to
    dnl # debug the configuration
    dnl #
    dnl define(`confLOG_LEVEL', `9')dnl
    dnl #
    dnl # Uncomment and edit the following line if your outgoing mail needs to
    dnl # be sent out through an external mail server:
    dnl #
>>  dnl # Use `smtp.comcast.net' on the next line as the SMART_HOST when using Comcast
>>  define(`SMART_HOST',`ganymede.lunarpages.com')dnl
>>  define(`RELAY_MAILER_ARGS', `TCP $h 587')
>>  define(`ESMTP_MAILER_ARGS', `TCP $h 587')
    dnl #
    define(`confDEF_USER_ID',``8:12'')dnl
    dnl define(`confAUTO_REBUILD')dnl
    define(`confTO_CONNECT', `1m')dnl
    define(`confTRY_NULL_MX_LIST',true)dnl
    define(`confDONT_PROBE_INTERFACES',true)dnl
    define(`PROCMAIL_MAILER_PATH',`/usr/bin/procmail')dnl
    define(`ALIAS_FILE', `/etc/aliases')dnl
    define(`STATUS_FILE', `/var/log/mail/statistics')dnl
    define(`UUCP_MAILER_MAX', `2000000')dnl
    define(`confUSERDB_SPEC', `/etc/mail/userdb.db')dnl
    define(`confPRIVACY_FLAGS', `authwarnings,novrfy,noexpn,restrictqrun')dnl
    define(`confAUTH_OPTIONS', `A')dnl
    dnl #
    dnl # The following allows relaying if the user authenticates, and disallows
    dnl # plaintext authentication (PLAIN/LOGIN) on non-TLS links
    dnl #
    dnl define(`confAUTH_OPTIONS', `A p')dnl
    dnl #
    dnl # PLAIN is the preferred plaintext authentication method and used by
    dnl # Mozilla Mail and Evolution, though Outlook Express and other MUAs do
    dnl # use LOGIN. Other mechanisms should be used if the connection is not
    dnl # guaranteed secure.
    dnl # Please remember that saslauthd needs to be running for AUTH.
    dnl #
    dnl TRUST_AUTH_MECH(`EXTERNAL DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')dnl
    dnl define(`confAUTH_MECHANISMS', `EXTERNAL GSSAPI DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')dnl
    dnl #
    dnl # Rudimentary information on creating certificates for sendmail TLS:
    dnl #     cd /usr/share/ssl/certs; make sendmail.pem
    dnl # Complete usage:
    dnl #     make -C /usr/share/ssl/certs usage
    dnl #
    dnl define(`confCACERT_PATH',`/etc/pki/tls/certs')dnl
    dnl define(`confCACERT',`/etc/pki/tls/certs/ca-bundle.crt')dnl
    dnl define(`confSERVER_CERT',`/etc/pki/tls/certs/sendmail.pem')dnl
    dnl define(`confSERVER_KEY',`/etc/pki/tls/certs/sendmail.pem')dnl
    dnl #
    dnl # This allows sendmail to use a keyfile that is shared with OpenLDAP's
    dnl # slapd, which requires the file to be readble by group ldap
    dnl #
    dnl define(`confDONT_BLAME_SENDMAIL',`groupreadablekeyfile')dnl
    dnl #
    dnl define(`confTO_QUEUEWARN', `4h')dnl
    dnl define(`confTO_QUEUERETURN', `5d')dnl
    dnl define(`confQUEUE_LA', `12')dnl
    dnl define(`confREFUSE_LA', `18')dnl
    define(`confTO_IDENT', `0')dnl
    dnl FEATURE(delay_checks)dnl
    FEATURE(`no_default_msa',`dnl')dnl
    FEATURE(`smrsh',`/usr/sbin/smrsh')dnl
>>  dnl # Uncomment the following line when Comcast is your SMART_HOST and authentication is required.
>>  dnl # You'll need to create the file referenced here (see the comments below this listing.)
>>  dnl FEATURE(`authinfo', `hash /etc/mail/authinfo')dnl
    FEATURE(`mailertable',`hash -o /etc/mail/mailertable.db')dnl
    FEATURE(`virtusertable',`hash -o /etc/mail/virtusertable.db')dnl
    FEATURE(redirect)dnl
    FEATURE(always_add_domain)dnl
    FEATURE(use_cw_file)dnl
    FEATURE(use_ct_file)dnl
    dnl #
    dnl # The following limits the number of processes sendmail can fork to accept
    dnl # incoming messages or process its message queues to 12.) sendmail refuses
    dnl # to accept connections once it has reached its quota of child processes.
    dnl #
    dnl define(`confMAX_DAEMON_CHILDREN', 12)dnl
    dnl #
    dnl # Limits the number of new connections per second. This caps the overhead
    dnl # incurred due to forking new sendmail processes. May be useful against
    dnl # DoS attacks or barrages of spam. (As mentioned below, a per-IP address
    dnl # limit would be useful but is not available as an option at this writing.)
    dnl #
    dnl define(`confCONNECTION_RATE_THROTTLE', 3)dnl
    dnl #
    dnl # The -t option will retry delivery if e.g. the user runs over his quota.
    dnl #
    FEATURE(local_procmail,`',`procmail -t -Y -a $h -d $u')dnl
    FEATURE(`access_db',`hash -T<TMPF> -o /etc/mail/access.db')dnl
    FEATURE(`blacklist_recipients')dnl
>>  dnl # EXPOSED_USER(`root')dnl
    dnl #
    dnl # For using Cyrus-IMAPd as POP3/IMAP server through LMTP delivery uncomment
    dnl # the following 2 definitions and activate below in the MAILER section the
    dnl # cyrusv2 mailer.
    dnl #
    dnl define(`confLOCAL_MAILER', `cyrusv2')dnl
    dnl define(`CYRUSV2_MAILER_ARGS', `FILE /var/lib/imap/socket/lmtp')dnl
    dnl #
    dnl # The following causes sendmail to only listen on the IPv4 loopback address
    dnl # 127.0.0.1 and not on any other network devices. Remove the loopback
    dnl # address restriction to accept email from the internet or intranet.
    dnl #
    DAEMON_OPTIONS(`Port=smtp,Addr=127.0.0.1, Name=MTA')dnl
    dnl #
    dnl # The following causes sendmail to additionally listen to port 587 for
    dnl # mail from MUAs that authenticate. Roaming users who can't reach their
    dnl # preferred sendmail daemon due to port 25 being blocked or redirected find
    dnl # this useful.
    dnl #
    dnl DAEMON_OPTIONS(`Port=submission, Name=MSA, M=Ea')dnl
    dnl #
    dnl # The following causes sendmail to additionally listen to port 465, but
    dnl # starting immediately in TLS mode upon connecting. Port 25 or 587 followed
    dnl # by STARTTLS is preferred, but roaming clients using Outlook Express can't
    dnl # do STARTTLS on ports other than 25. Mozilla Mail can ONLY use STARTTLS
    dnl # and doesn't support the deprecated smtps; Evolution <1.1.1 uses smtps
    dnl # when SSL is enabled-- STARTTLS support is available in version 1.1.1.
    dnl #
    dnl # For this to work your OpenSSL certificates must be configured.
    dnl #
    dnl DAEMON_OPTIONS(`Port=smtps, Name=TLSMTA, M=s')dnl
    dnl #
    dnl # The following causes sendmail to additionally listen on the IPv6 loopback
    dnl # device. Remove the loopback address restriction listen to the network.
    dnl #
    dnl DAEMON_OPTIONS(`port=smtp,Addr=::1, Name=MTA-v6, Family=inet6')dnl
    dnl #
    dnl # enable both ipv6 and ipv4 in sendmail:
    dnl #
    dnl DAEMON_OPTIONS(`Name=MTA-v4, Family=inet, Name=MTA-v6, Family=inet6')
    dnl #
    dnl # We strongly recommend not accepting unresolvable domains if you want to
    dnl # protect yourself from spam. However, the laptop and users on computers
    dnl # that do not have 24x7 DNS do need this.
    dnl #
    FEATURE(`accept_unresolvable_domains')dnl
    dnl #
    dnl FEATURE(`relay_based_on_MX')dnl
    dnl #
    dnl # Also accept email sent to "localhost.localdomain" as local email.
    dnl #
    LOCAL_DOMAIN(`localhost.localdomain')dnl
    dnl #
    dnl # The following example makes mail from this host and any additional
    dnl # specified domains appear to be sent from mydomain.com
    dnl #
>>  MASQUERADE_AS(`daveking.com')dnl
    dnl #
    dnl # masquerade not just the headers, but the envelope as well
    dnl #
>>  FEATURE(masquerade_envelope)dnl
    dnl #
    dnl # masquerade not just @mydomainalias.com, but @*.mydomainalias.com as well
    dnl #
>>  FEATURE(masquerade_entire_domain)dnl
    dnl #
>>  FEATURE(allmasquerade)dnl
    dnl #
    dnl MASQUERADE_DOMAIN(localhost)dnl
    dnl MASQUERADE_DOMAIN(localhost.localdomain)dnl
    dnl MASQUERADE_DOMAIN(mydomainalias.com)dnl
    dnl MASQUERADE_DOMAIN(mydomain.lan)dnl
>>  MASQUERADE_DOMAIN(fang.localdomain)dnl
    MAILER(smtp)dnl
    MAILER(procmail)dnl
    dnl MAILER(cyrusv2)dnl

Then, to activate these changes:

service sendmail restart

Mail for the root user can be redirected by specifying an alias for the root userid in the file /etc/aliases. Uncomment and set the alias for root at the bottom of /etc/aliases and then run the command “newaliases”.

Note: The command “sendmail -d0.1 -bv” shows the version of sendmail in use.

The /etc/mail/authinfo File

The /etc/mail/authinfo file referenced in the /etc/mail/sendmail.mc listing above contains the authentication information required to access the Cmcast SMTP server at port 587. This is your main Comcast userid and password. In the example below "dlkiii" is my userid and "987654321" is my password:

AuthInfo:smtp.comcast.net "U:smmsp" "I:dlkiii" "P:987654321" "M:PLAIN"