sender_email - email address that does not exist, but must be used as FROM address, because receiver host rejects emails from other emails.

receiver_email - email that is supposed to receive the sent message

local_smtp - SMTP server that is installed on another computer in the local network and forwards all received messages to external_smtp

external_smtp - SMTP server that is installed on a computer in another network and rejects all emails that do not come from sender_email

I have configured sendmail to send emails from sender_email and authenticate with user/password to local_smtp that is supposed to send the email message further to external_smtp that only accepts emails sent from a specific email, which is sender_email in this case. However, judging from the log files sendmail authenticates with external_smtp instead of local_smtp. I do not want to authenticate with external_smtp, because that is up to local_smtp.


10745 <<< Subject: Terminal Email Send
10745 <<<
10745 <<< Email Content line 1
10745 <<< Email Content line 2
10745 <<< [EOF]
10759 === CONNECT local_smtp.
10759 <<< 220 **********************************************************************^M
10759 >>> EHLO mgmt-snmp
10759 <<< 250-local_smtp says hello^M
10759 <<< 250-AUTH LOGIN PLAIN^M
10759 <<< 250-VRFY^M
10759 <<< 250 8BITMIME^M
10759 >>> MAIL From:<sender_email> AUTH=sender_email
10759 <<< 530 authentication required^M
10759 >>> This is a MIME-encapsulated message
10759 >>>
10759 >>> --t8IEdmbX010759.1442587188/mgmt-snmp
10759 >>>
10759 >>> The original message was received at Fri, 18 Sep 2015 16:39:48 +0200
10759 >>> from root@localhost
10759 >>>
10759 >>>    ----- The following addresses had permanent fatal errors -----
10759 >>> receiver_email
10759 >>>     (reason: 530 authentication required)
10759 >>>

I guess it has something to do with AUTH=sender_email, but I do not know how to change it.


# $Sendmail: debproto.mc,v 8.14.4 2014-02-11 13:02:08 cowboy Exp $
# Copyright (c) 1998-2010 Richard Nelson.  All Rights Reserved.
# cf/debian/sendmail.mc.  Generated from sendmail.mc.in by configure.
# sendmail.mc prototype config file for building Sendmail 8.14.4
# Note: the .in file supports 8.7.6 - 9.0.0, but the generated
#   file is customized to the version noted above.
# This file is used to configure Sendmail for use with Debian systems.
# If you modify this file, you will have to regenerate /etc/mail/sendmail.cf
# by running this file through the m4 preprocessor via one of the following:
#   * make   (or make -C /etc/mail)
#   * sendmailconfig 
#   * m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf
# The first two options are preferred as they will also update other files
# that depend upon the contents of this file.
# The best documentation for this .mc file is:
# /usr/share/doc/sendmail-doc/cf.README.gz
#   Copyright (c) 1998-2005 Richard Nelson.  All Rights Reserved.
#  This file is used to configure Sendmail for use with Debian systems.
VERSIONID(`$Id: sendmail.mc, v 8.14.4-4.1ubuntu1 2014-02-11 13:02:08 cowboy Exp $')
dnl # Items controlled by /etc/mail/sendmail.conf - DO NOT TOUCH HERE
dnl # Items controlled by /etc/mail/sendmail.conf - DO NOT TOUCH HERE
dnl #
dnl # General defines
dnl #
dnl # SAFE_FILE_ENV: [undefined] If set, sendmail will do a chroot()
dnl #   into this directory before writing files.
dnl #   If *all* your user accounts are under /home then use that
dnl #   instead - it will prevent any writes outside of /home !
dnl #   define(`confSAFE_FILE_ENV',             `')dnl
dnl #
dnl # Daemon options - restrict to servicing LOCALHOST ONLY !!!
dnl # Remove `, Addr=' clauses to receive from any interface
dnl # If you want to support IPv6, switch the commented/uncommentd lines
dnl #
dnl DAEMON_OPTIONS(`Family=inet6, Name=MTA-v6, Port=smtp, Addr=::1')dnl
DAEMON_OPTIONS(`Family=inet,  Name=MTA-v4, Port=smtp')dnl
dnl DAEMON_OPTIONS(`Family=inet6, Name=MSP-v6, Port=submission, M=Ea, Addr=::1')dnl
DAEMON_OPTIONS(`Family=inet,  Name=MSP-v4, Port=submission, M=Ea, Addr=')dnl
dnl #
dnl # Be somewhat anal in what we allow
dnl #
dnl # Define connection throttling and window length
define(`confCONNECTION_RATE_THROTTLE', `15')dnl
dnl #
dnl # Features
dnl #
dnl # use /etc/mail/local-host-names
dnl #
dnl # The access db is the basis for most of sendmail's checking
FEATURE(`access_db', , `skip')dnl
dnl #
dnl # The greet_pause feature stops some automail bots - but check the
dnl # provided access db for details on excluding localhosts...
FEATURE(`greet_pause', `1000')dnl 1 seconds
dnl #
dnl # Delay_checks allows sender<->recipient checking
FEATURE(`delay_checks', `friend', `n')dnl
dnl #
dnl # If we get too many bad recipients, slow things down...
dnl #
dnl # Stop connections that overflow our concurrent and time connection rates
FEATURE(`conncontrol', `nodelay', `terminate')dnl
FEATURE(`ratecontrol', `nodelay', `terminate')dnl
dnl #
dnl # If you're on a dialup link, you should enable this - so sendmail
dnl # will not bring up the link (it will queue mail for later)
dnl define(`confCON_EXPENSIVE',`True')dnl
dnl #
dnl # Dialup/LAN connection overrides
dnl #

dnl EXPOSED_USER(root uucp)dnl # users exempt from masquerading
dnl LOCAL_USER(root)dnl
dnl MASQUERADE_AS(`external_smtp')dnl
dnl FEATURE(`allmasquerade')dnl
dnl FEATURE(`masquerade_envelope')dnl
dnl FEATURE(`nullclient', local_smtp)dnl

## Custom configurations below (will be preserved)
define(`SMART_HOST', `local_smtp')dnl
FEATURE(`authinfo', `hash /etc/mail/authinfo')dnl
define(`RELAY_MAILER_ARGS', `TCP $h 25')dnl
dnl #
dnl # Default Mailer setup


AuthInfo:local_smtp "U:root" "I:my_username" "P:my_password"
  • Looks like whatever is connecting to local_smtp is not authenticating, as it did not issue an AUTH verb, and instead issued a MAIL FROM, which local_smtp then shot down. Is the MTA on whatever is connecting to local_smtp properly configured to authenticate as a client? – thrig Sep 18 '15 at 15:49
  • I use sendmail for authentication and it is configured in sendmail.mc file: FEATURE(``authinfo', ``hash /etc/mail/authinfo')dnl – Jonas Hoffmann Sep 18 '15 at 16:24
  • But it did use AUTH for local_smtp: 10759 <<< 250-AUTH LOGIN PLAIN^M. Or is this not it? – Jonas Hoffmann Sep 21 '15 at 7:43
  • That's the banner from the server. Had the client authenticated, I would expect to see a response >>> AUTH .... Instead, there is a >>> MAIL ... line. – thrig Sep 21 '15 at 14:27

As root send a test message with tracking map (authinfo) lookups.

# -d60.5 turn on traking map lookups
/usr/sbin/sendmail -d60.5 -v -i -fsender_email -- receiver_email  <<END
subject: test


Possible outcomes to define next tests:

  • no authinfo lookups
  • authinfo lookups with keys other than you expected
  • authinfo lookups returning "no match"
  • authinfo lookups returning correct values

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