xref: /freebsd/contrib/sendmail/README (revision d39bd2c1388b520fcba9abed1932acacead60fba)

			SENDMAIL RELEASE 8

This directory has the latest sendmail(TM) software from Proofpoint, Inc.

Report any bugs to sendmail-bugs-YYYY@support.sendmail.org
where YYYY is the current year, e.g., 2023.

There is a web site at https://www.sendmail.org/ -- see that site for
the latest updates.


+--------------+
| INTRODUCTION |
+--------------+

0. The vast majority of queries about sendmail are answered in the
   README files noted below.

1. Read this README file, especially this introduction, and the DIRECTORY
   PERMISSIONS sections.

2. Read the INSTALL file in this directory.

3. Read sendmail/README, especially:
   a. the introduction
   b. the BUILDING SENDMAIL section
   c. the relevant part(s) of the OPERATING SYSTEM AND COMPILE QUIRKS section

   You may also find these useful:

   d. sendmail/SECURITY
   e. devtools/README
   f. devtools/Site/README
   g. libmilter/README
   h. mail.local/README
   i. smrsh/README

4. Read cf/README.

Sendmail is a trademark of Proofpoint, Inc.
US Patent Numbers 6865671, 6986037.


+-----------------------+
| DIRECTORY PERMISSIONS |
+-----------------------+

Sendmail often gets blamed for many problems that are actually the
result of other problems, such as overly permissive modes on directories.
For this reason, sendmail checks the modes on system directories and
files to determine if they can be trusted.  For sendmail to run without
complaining, you MUST execute the following command:

	chmod go-w / /etc /etc/mail /usr /var /var/spool /var/spool/mqueue
	chown root / /etc /etc/mail /usr /var /var/spool /var/spool/mqueue

You will probably have to tweak this for your environment (for example,
some systems put the spool directory into /usr/spool instead of
/var/spool).  If you set the RunAsUser option in your sendmail.cf, the
/var/spool/mqueue directory will have to be owned by the RunAsUser user.
As a general rule, after you have compiled sendmail, run the command

	sendmail -v -bi

to initialize the alias database.  If it gives messages such as

	WARNING: writable directory /etc
	WARNING: writable directory /var/spool/mqueue

then the directories listed have inappropriate write permissions and
should be secured to avoid various possible security attacks.

Beginning with sendmail 8.9, these checks have become more strict to
prevent users from being able to access files they would normally not
be able to read.  In particular, .forward and :include: files in unsafe
directory paths (directory paths which are group or world writable) will
no longer be allowed.  This would mean that if user joe's home directory
was writable by group staff, sendmail would not use his .forward file.
This behavior can be altered, at the expense of system security, by
setting the DontBlameSendmail option.  For example, to allow .forward
files in group writable directories:

	O DontBlameSendmail=forwardfileingroupwritabledirpath

Or to allow them in both group and world writable directories:

	O DontBlameSendmail=forwardfileinunsafedirpath

Items from these unsafe .forward and :include: files will be marked
as unsafe addresses -- the items can not be deliveries to files or
programs.  This behavior can also be altered via DontBlameSendmail:

	O DontBlameSendmail=forwardfileinunsafedirpath,
		forwardfileinunsafedirpathsafe

The first flag allows the .forward file to be read, the second allows
the items in the file to be marked as safe for file and program
delivery.

Other files affected by this strengthened security include class
files (i.e., Fw /etc/mail/local-host-names), persistent host status files,
and the files specified by the ErrorHeader and HelpFile options.  Similar
DontBlameSendmail flags are available for the class, ErrorHeader, and
HelpFile files.

If you have an unsafe configuration of .forward and :include:
files, you can make it safe by finding all such files, and doing
a "chmod go-w $FILE" on each.  Also, do a "chmod go-w $DIR" for
each directory in the file's path.


+--------------------------+
| FILE AND MAP PERMISSIONS |
+--------------------------+

Any application which uses either flock() or fcntl() style locking or
other APIs that use one of these locking methods (such as open() with
O_EXLOCK and O_SHLOCK) on files readable by other local untrusted users
may be susceptible to local denial of service attacks.

File locking is used throughout sendmail for a variety of files
including aliases, maps, statistics, and the pid file.  Any user who
can open one of these files can prevent sendmail or it's associated
utilities, e.g., makemap or newaliases, from operating properly.  This
can also affect sendmail's ability to update status files such as
statistics files.  For system which use flock() for file locking, a
user's ability to obtain an exclusive lock prevents other sendmail
processes from reading certain files such as alias or map databases.

A workaround for this problem is to protect all sendmail files such
that they can't be opened by untrusted users.  As long as users can
not open a file, they can not lock it.  Since queue files should
already have restricted permissions, the only files that need
adjustment are alias, map, statistics, and pid files.  These files
should be owned by root or the trusted user specified in the
TrustedUser option.  Changing the permissions to be only readable and
writable by that user is sufficient to avoid the denial of service.
For example, depending on the paths you use, these commands would be
used:

	chmod 0640 /etc/mail/aliases /etc/mail/aliases.{db,pag,dir}
	chmod 0640 /etc/mail/*.{db,pag,dir}
	chmod 0640 /etc/mail/statistics /var/log/sendmail.st
	chmod 0600 /var/run/sendmail.pid /etc/mail/sendmail.pid

If the permissions 0640 are used, be sure that only trusted users belong
to the group assigned to those files.  Otherwise, files should not even
be group readable.  As of sendmail 8.12.4, the permissions shown above
are the default permissions for newly created files.

Note that the denial of service on the plain text aliases file
(/etc/mail/aliases) only prevents newaliases from rebuilding the
aliases file.  The same is true for the database files on systems which
use fcntl() style locking.  Since it does not interfere with normal
operations, sites may chose to leave these files readable.  Also, it is
not necessary to protect the text files associated with map databases
as makemap does not lock those files.


+-----------------------+
| RELATED DOCUMENTATION |
+-----------------------+

There are other files you should read.  Rooted in this directory are:

  FAQ
	The FAQ (frequently answered questions) is no longer maintained
	with the sendmail release.  It is available at
	http://www.sendmail.org/faq/ .  The file FAQ is a reminder of
	this and a pointer to the web page.
  INSTALL
	Installation instructions for building and installing sendmail.
  KNOWNBUGS
	Known bugs in the current release.
  RELEASE_NOTES
	A detailed description of the changes in each version.  This
	is quite long, but informative.
  sendmail/README
	Details on compiling and installing sendmail.
  cf/README
	Details on configuring sendmail.
  doc/op/op.me
	The sendmail Installation & Operations Guide.  In addition
	to the shipped PostScript version, plain text and PDF versions
	can be generating using (assuming the required conversion software
	is installed on your system, see doc/op/Makefile):

	cd doc/op && make op.txt op.pdf

	Be warned: on some systems calling make in doc/op/ will cause
	errors due to nroff/groff problems.  Known problems are:
	- running this off on systems with an old version of -me, you
	need to add the following macro to the macros:

		.de sm
		\s-1\\$1\\s0\\$2
		..

	This sets a word in a smaller pointsize.


+--------------+
| RELATED RFCS |
+--------------+

There are several related RFCs that you may wish to read -- they are
available from several sites, see

	http://www.rfc-editor.org/
	http://www.ietf.org/

Important RFCs for electronic mail are:

	RFC821	SMTP protocol
	RFC822	Mail header format
	RFC974	MX routing
	RFC976	UUCP mail format
	RFC1123	Host requirements (modifies 821, 822, and 974)
	RFC1344	Implications of MIME for Internet Mail Gateways
	RFC1413	Identification server
	RFC1428	Transition of Internet Mail from Just-Send-8 to
		8-bit SMTP/MIME
	RFC1652	SMTP Service Extension for 8bit-MIMEtransport
	RFC1869	SMTP Service Extensions (ESMTP spec)
	RFC1870	SMTP Service Extension for Message Size Declaration
	RFC1891	SMTP Service Extension for Delivery Status Notifications
	RFC1892	Multipart/Report Content Type for the Reporting of
		Mail System Administrative Messages
	RFC1893	Enhanced Mail System Status Codes
	RFC1894	An Extensible Message Format for Delivery Status
		Notifications
	RFC1985	SMTP Service Extension for Remote Message Queue Starting
	RFC2033 Local Mail Transfer Protocol (LMTP)
	RFC2034 SMTP Service Extension for Returning Enhanced Error Codes
	RFC2045	Multipurpose Internet Mail Extensions (MIME) Part One:
		Format of Internet Message Bodies
	RFC2476 Message Submission
	RFC2487 SMTP Service Extension for Secure SMTP over TLS
	RFC2554 SMTP Service Extension for Authentication
	RFC2821 Simple Mail Transfer Protocol
	RFC2822 Internet Message Format
	RFC2852 Deliver By SMTP Service Extension
	RFC2920 SMTP Service Extension for Command Pipelining
	RFC5321 Simple Mail Transfer Protocol
	RFC5322 Internet Message Format
	RFC6530 Overview and Framework for Internationalized Email
	RFC6531 SMTP Extension for Internationalized Email
	RFC6532 Internationalized Email Headers
	RFC6533 Internationalized Delivery Status and Disposition Notifications
	RFC8461 SMTP MTA Strict Transport Security (MTA-STS)

Other standards that may be of interest (but which are less directly
relevant to sendmail) are:

	RFC987	Mapping between RFC822 and X.400
	RFC1049	Content-Type header field (extension to RFC822)

Warning to AIX users: this version of sendmail does not implement
MB, MR, or MG DNS resource records, as defined (as experiments) in
RFC1035.


+---------+
| WARNING |
+---------+

Since sendmail 8.11 and later includes hooks to cryptography, the
following information from OpenSSL applies to sendmail as well.

PLEASE REMEMBER THAT EXPORT/IMPORT AND/OR USE OF STRONG CRYPTOGRAPHY
SOFTWARE, PROVIDING CRYPTOGRAPHY HOOKS OR EVEN JUST COMMUNICATING
TECHNICAL DETAILS ABOUT CRYPTOGRAPHY SOFTWARE IS ILLEGAL IN SOME
PARTS OF THE WORLD.  SO, WHEN YOU IMPORT THIS PACKAGE TO YOUR
COUNTRY, RE-DISTRIBUTE IT FROM THERE OR EVEN JUST EMAIL TECHNICAL
SUGGESTIONS OR EVEN SOURCE PATCHES TO THE AUTHOR OR OTHER PEOPLE
YOU ARE STRONGLY ADVISED TO PAY CLOSE ATTENTION TO ANY EXPORT/IMPORT
AND/OR USE LAWS WHICH APPLY TO YOU.  THE AUTHORS ARE NOT LIABLE FOR
ANY VIOLATIONS YOU MAKE HERE.  SO BE CAREFUL, IT IS YOUR RESPONSIBILITY.

If you use OpenSSL then make sure you read their README file which
contains information about patents etc.


+-------------------+
| DATABASE ROUTINES |
+-------------------+

IF YOU WANT TO RUN THE NEW BERKELEY DB SOFTWARE:  ****  DO NOT  ****
use the version that was on the Net2 tape -- it has a number of
nefarious bugs that were bad enough when I got them; you shouldn't have
to go through the same thing.  Instead, get a new version via the web at
http://www.sleepycat.com/.  This software is highly recommended; it gets
rid of several stupid limits, it's much faster, and the interface is
nicer to animals and plants.  If the Berkeley DB include files
are installed in a location other than those which your compiler searches,
you will need to provide that directory when building:

	./Build -I/path/to/include/directory

If you are using Berkeley DB versions 1.85 or 1.86, you are *strongly*
urged to upgrade to DB version 2 or later, available from
http://www.sleepycat.com/.  Berkeley DB versions 1.85 and 1.86 are known to
be broken in various nasty ways (see http://www.sleepycat.com/db.185.html),
and can cause sendmail to dump core.  In addition, the newest versions of
gcc and the Solaris compilers perform optimizations in those versions that
may cause fairly random core dumps.

If you have no choice but to use Berkeley DB 1.85 or 1.86, and you are
using both Berkeley DB and files in the UNIX ndbm format, remove ndbm.h
and ndbm.o from the DB library after building it.  You should also apply
all of the patches for DB 1.85 and 1.86 found at the Sleepycat web site
(see http://www.sleepycat.com/db.185.html), as they fix some of the known
problems.

If you are using a version of Berkeley DB 2 previous to 2.3.15, and you
are using both Berkeley DB and files in the UNIX ndbm format, remove dbm.o
from the DB library after building it.  No other changes are necessary.

If you are using Berkeley DB version 2.3.15 or greater, no changes are
necessary.

The underlying database file formats changed between Berkeley DB versions
1.85 and 1.86, again between DB 1.86 and version 2.0, and finally between
DB 2.X and 3.X.  If you are upgrading from one of those versions, you must
recreate your database file(s).  Do this by rebuilding all maps with
makemap and rebuilding the alias file with newaliases.

File locking using fcntl() does not interoperate with Berkeley DB
5.x (and probably later).  Use CDB, flock() (-DHASFLOCK), or an
earlier Berkeley DB version.


+--------------------+
| HOST NAME SERVICES |
+--------------------+

If you are using NIS or /etc/hosts, it is critical that you
list the long (fully qualified) name somewhere (preferably first) in
the /etc/hosts file used to build the NIS database.  For example, the
line should read

	128.32.149.68   mastodon.CS.Berkeley.EDU mastodon

**** NOT ****

	128.32.149.68   mastodon

If you do not include the long name, sendmail will complain loudly
about ``unable to qualify my own domain name (mastodon) -- using
short name'' and conclude that your canonical name is the short
version and use that in messages.  The name "mastodon" doesn't mean
much outside of Berkeley, and so this creates incorrect and unreplyable
messages.


+-------------+
| USE WITH MH |
+-------------+

This version of sendmail notices and reports certain kinds of SMTP
protocol violations that were ignored by older versions.  If you
are running MH you may wish to install the patch in contrib/mh.patch
that will prevent these warning reports.  This patch also works
with the old version of sendmail, so it's safe to go ahead and
install it.


+----------------+
| USE WITH IDENT |
+----------------+

Sendmail 8 supports the IDENT protocol, as defined by RFC 1413.
Note that the RFC states a client should wait at least 30 seconds
for a response.  As of 8.10.0, the default Timeout.ident is 5 seconds
as many sites have adopted the practice of dropping IDENT queries.
This has lead to delays processing mail.


+-------------------------+
| INTEROPERATION PROBLEMS |
+-------------------------+

Microsoft Exchange Server 5.0
	We have had a report that ``about 7% of messages from Sendmail
	to Exchange were not being delivered with status messages of
	"connection reset" and "I/O error".''  Upgrading Exchange from
	Version 5.0 to Version 5.5 Service Pack 2 solved this problem.

CommuniGate Pro
	CommuniGate Pro 3.2.4 does not accept the AUTH= -parameter on
	the MAIL FROM command if the client is not authenticated.  Use

		define(`confAUTH_OPTIONS', `A')

	in .mc file if you have compiled sendmail with Cyrus SASL
	and you communicate with CommuniGate Pro servers.


+---------------------+
| DIRECTORY STRUCTURE |
+---------------------+

The structure of this directory tree is:

cf		Source for sendmail configuration files.  These are
		different than what you've seen before.  They are a
		fairly dramatic rewrite, requiring the new sendmail
		(since they use new features).
contrib		Some contributed tools to help with sendmail.  THESE
		ARE NOT SUPPORTED by sendmail -- contact the original
		authors if you have problems.  (This directory is not
		on the 4.4BSD tape.)
devtools	Build environment.  See devtools/README.
doc		Documentation.  If you are getting source, read
		op.me -- it's long, but worth it.
editmap		A program to edit and query maps that have been created
		with makemap, e.g., adding and deleting entries.
include		Include files used by multiple programs in the distribution.
libsmdb		sendmail database library with support for Berkeley DB 1.X,
		Berkeley DB 2.X, Berkeley DB 3.X, and NDBM.
libsmutil	sendmail utility library with functions used by different
		programs.
mail.local	The source for the local delivery agent used for 4.4BSD.
		THIS IS NOT PART OF SENDMAIL! and may not compile
		everywhere, since it depends on some 4.4-isms.  Warning:
		it does mailbox locking differently than other systems.
mailstats	Statistics printing program.
makemap		A program that creates the keyed maps used by the $( ... $)
		construct in sendmail.  It is primitive but effective.
		It takes a very simple input format, so you will probably
		expect to preprocess must human-convenient formats
		using sed scripts before this program will like them.
		But it should be functionally complete.
praliases	A program to print the map version of the aliases file.
rmail		Source for rmail(8).  This is used as a delivery
		agent for for UUCP, and could presumably be used by
		other non-socket oriented mailers.  Older versions of
		rmail are probably deficient.  RMAIL IS NOT PART OF
		SENDMAIL!!!  The 4.4BSD source is included for you to
		look at or try to port to your system.  There is no
		guarantee it will even compile on your operating system.
smrsh		The "sendmail restricted shell", which can be used as
		a replacement for /bin/sh in the prog mailer to provide
		increased security control.  NOT PART OF SENDMAIL!
sendmail	Source for the sendmail program itself.
test		Some test scripts (currently only for compilation aids).
vacation	Source for the vacation program.  NOT PART OF SENDMAIL!