1 2 SENDMAIL RELEASE 8 3 4This directory has the latest sendmail(TM) software from Proofpoint, Inc. 5 6Report any bugs to sendmail-bugs-YYYY@support.sendmail.org 7where YYYY is the current year, e.g., 2023. 8 9There is a web site at https://www.sendmail.org/ -- see that site for 10the latest updates. 11 12 13+--------------+ 14| INTRODUCTION | 15+--------------+ 16 170. The vast majority of queries about sendmail are answered in the 18 README files noted below. 19 201. Read this README file, especially this introduction, and the DIRECTORY 21 PERMISSIONS sections. 22 232. Read the INSTALL file in this directory. 24 253. Read sendmail/README, especially: 26 a. the introduction 27 b. the BUILDING SENDMAIL section 28 c. the relevant part(s) of the OPERATING SYSTEM AND COMPILE QUIRKS section 29 30 You may also find these useful: 31 32 d. sendmail/SECURITY 33 e. devtools/README 34 f. devtools/Site/README 35 g. libmilter/README 36 h. mail.local/README 37 i. smrsh/README 38 394. Read cf/README. 40 41Sendmail is a trademark of Proofpoint, Inc. 42US Patent Numbers 6865671, 6986037. 43 44 45+-----------------------+ 46| DIRECTORY PERMISSIONS | 47+-----------------------+ 48 49Sendmail often gets blamed for many problems that are actually the 50result of other problems, such as overly permissive modes on directories. 51For this reason, sendmail checks the modes on system directories and 52files to determine if they can be trusted. For sendmail to run without 53complaining, you MUST execute the following command: 54 55 chmod go-w / /etc /etc/mail /usr /var /var/spool /var/spool/mqueue 56 chown root / /etc /etc/mail /usr /var /var/spool /var/spool/mqueue 57 58You will probably have to tweak this for your environment (for example, 59some systems put the spool directory into /usr/spool instead of 60/var/spool). If you set the RunAsUser option in your sendmail.cf, the 61/var/spool/mqueue directory will have to be owned by the RunAsUser user. 62As a general rule, after you have compiled sendmail, run the command 63 64 sendmail -v -bi 65 66to initialize the alias database. If it gives messages such as 67 68 WARNING: writable directory /etc 69 WARNING: writable directory /var/spool/mqueue 70 71then the directories listed have inappropriate write permissions and 72should be secured to avoid various possible security attacks. 73 74Beginning with sendmail 8.9, these checks have become more strict to 75prevent users from being able to access files they would normally not 76be able to read. In particular, .forward and :include: files in unsafe 77directory paths (directory paths which are group or world writable) will 78no longer be allowed. This would mean that if user joe's home directory 79was writable by group staff, sendmail would not use his .forward file. 80This behavior can be altered, at the expense of system security, by 81setting the DontBlameSendmail option. For example, to allow .forward 82files in group writable directories: 83 84 O DontBlameSendmail=forwardfileingroupwritabledirpath 85 86Or to allow them in both group and world writable directories: 87 88 O DontBlameSendmail=forwardfileinunsafedirpath 89 90Items from these unsafe .forward and :include: files will be marked 91as unsafe addresses -- the items can not be deliveries to files or 92programs. This behavior can also be altered via DontBlameSendmail: 93 94 O DontBlameSendmail=forwardfileinunsafedirpath, 95 forwardfileinunsafedirpathsafe 96 97The first flag allows the .forward file to be read, the second allows 98the items in the file to be marked as safe for file and program 99delivery. 100 101Other files affected by this strengthened security include class 102files (i.e., Fw /etc/mail/local-host-names), persistent host status files, 103and the files specified by the ErrorHeader and HelpFile options. Similar 104DontBlameSendmail flags are available for the class, ErrorHeader, and 105HelpFile files. 106 107If you have an unsafe configuration of .forward and :include: 108files, you can make it safe by finding all such files, and doing 109a "chmod go-w $FILE" on each. Also, do a "chmod go-w $DIR" for 110each directory in the file's path. 111 112 113+--------------------------+ 114| FILE AND MAP PERMISSIONS | 115+--------------------------+ 116 117Any application which uses either flock() or fcntl() style locking or 118other APIs that use one of these locking methods (such as open() with 119O_EXLOCK and O_SHLOCK) on files readable by other local untrusted users 120may be susceptible to local denial of service attacks. 121 122File locking is used throughout sendmail for a variety of files 123including aliases, maps, statistics, and the pid file. Any user who 124can open one of these files can prevent sendmail or it's associated 125utilities, e.g., makemap or newaliases, from operating properly. This 126can also affect sendmail's ability to update status files such as 127statistics files. For system which use flock() for file locking, a 128user's ability to obtain an exclusive lock prevents other sendmail 129processes from reading certain files such as alias or map databases. 130 131A workaround for this problem is to protect all sendmail files such 132that they can't be opened by untrusted users. As long as users can 133not open a file, they can not lock it. Since queue files should 134already have restricted permissions, the only files that need 135adjustment are alias, map, statistics, and pid files. These files 136should be owned by root or the trusted user specified in the 137TrustedUser option. Changing the permissions to be only readable and 138writable by that user is sufficient to avoid the denial of service. 139For example, depending on the paths you use, these commands would be 140used: 141 142 chmod 0640 /etc/mail/aliases /etc/mail/aliases.{db,pag,dir} 143 chmod 0640 /etc/mail/*.{db,pag,dir} 144 chmod 0640 /etc/mail/statistics /var/log/sendmail.st 145 chmod 0600 /var/run/sendmail.pid /etc/mail/sendmail.pid 146 147If the permissions 0640 are used, be sure that only trusted users belong 148to the group assigned to those files. Otherwise, files should not even 149be group readable. As of sendmail 8.12.4, the permissions shown above 150are the default permissions for newly created files. 151 152Note that the denial of service on the plain text aliases file 153(/etc/mail/aliases) only prevents newaliases from rebuilding the 154aliases file. The same is true for the database files on systems which 155use fcntl() style locking. Since it does not interfere with normal 156operations, sites may chose to leave these files readable. Also, it is 157not necessary to protect the text files associated with map databases 158as makemap does not lock those files. 159 160 161+-----------------------+ 162| RELATED DOCUMENTATION | 163+-----------------------+ 164 165There are other files you should read. Rooted in this directory are: 166 167 FAQ 168 The FAQ (frequently answered questions) is no longer maintained 169 with the sendmail release. It is available at 170 http://www.sendmail.org/faq/ . The file FAQ is a reminder of 171 this and a pointer to the web page. 172 INSTALL 173 Installation instructions for building and installing sendmail. 174 KNOWNBUGS 175 Known bugs in the current release. 176 RELEASE_NOTES 177 A detailed description of the changes in each version. This 178 is quite long, but informative. 179 sendmail/README 180 Details on compiling and installing sendmail. 181 cf/README 182 Details on configuring sendmail. 183 doc/op/op.me 184 The sendmail Installation & Operations Guide. In addition 185 to the shipped PostScript version, plain text and PDF versions 186 can be generating using (assuming the required conversion software 187 is installed on your system, see doc/op/Makefile): 188 189 cd doc/op && make op.txt op.pdf 190 191 Be warned: on some systems calling make in doc/op/ will cause 192 errors due to nroff/groff problems. Known problems are: 193 - running this off on systems with an old version of -me, you 194 need to add the following macro to the macros: 195 196 .de sm 197 \s-1\\$1\\s0\\$2 198 .. 199 200 This sets a word in a smaller pointsize. 201 202 203+--------------+ 204| RELATED RFCS | 205+--------------+ 206 207There are several related RFCs that you may wish to read -- they are 208available from several sites, see 209 210 http://www.rfc-editor.org/ 211 http://www.ietf.org/ 212 213Important RFCs for electronic mail are: 214 215 RFC821 SMTP protocol 216 RFC822 Mail header format 217 RFC974 MX routing 218 RFC976 UUCP mail format 219 RFC1123 Host requirements (modifies 821, 822, and 974) 220 RFC1344 Implications of MIME for Internet Mail Gateways 221 RFC1413 Identification server 222 RFC1428 Transition of Internet Mail from Just-Send-8 to 223 8-bit SMTP/MIME 224 RFC1652 SMTP Service Extension for 8bit-MIMEtransport 225 RFC1869 SMTP Service Extensions (ESMTP spec) 226 RFC1870 SMTP Service Extension for Message Size Declaration 227 RFC1891 SMTP Service Extension for Delivery Status Notifications 228 RFC1892 Multipart/Report Content Type for the Reporting of 229 Mail System Administrative Messages 230 RFC1893 Enhanced Mail System Status Codes 231 RFC1894 An Extensible Message Format for Delivery Status 232 Notifications 233 RFC1985 SMTP Service Extension for Remote Message Queue Starting 234 RFC2033 Local Mail Transfer Protocol (LMTP) 235 RFC2034 SMTP Service Extension for Returning Enhanced Error Codes 236 RFC2045 Multipurpose Internet Mail Extensions (MIME) Part One: 237 Format of Internet Message Bodies 238 RFC2476 Message Submission 239 RFC2487 SMTP Service Extension for Secure SMTP over TLS 240 RFC2554 SMTP Service Extension for Authentication 241 RFC2821 Simple Mail Transfer Protocol 242 RFC2822 Internet Message Format 243 RFC2852 Deliver By SMTP Service Extension 244 RFC2920 SMTP Service Extension for Command Pipelining 245 RFC5321 Simple Mail Transfer Protocol 246 RFC5322 Internet Message Format 247 RFC6530 Overview and Framework for Internationalized Email 248 RFC6531 SMTP Extension for Internationalized Email 249 RFC6532 Internationalized Email Headers 250 RFC6533 Internationalized Delivery Status and Disposition Notifications 251 RFC8461 SMTP MTA Strict Transport Security (MTA-STS) 252 253Other standards that may be of interest (but which are less directly 254relevant to sendmail) are: 255 256 RFC987 Mapping between RFC822 and X.400 257 RFC1049 Content-Type header field (extension to RFC822) 258 259Warning to AIX users: this version of sendmail does not implement 260MB, MR, or MG DNS resource records, as defined (as experiments) in 261RFC1035. 262 263 264+---------+ 265| WARNING | 266+---------+ 267 268Since sendmail 8.11 and later includes hooks to cryptography, the 269following information from OpenSSL applies to sendmail as well. 270 271PLEASE REMEMBER THAT EXPORT/IMPORT AND/OR USE OF STRONG CRYPTOGRAPHY 272SOFTWARE, PROVIDING CRYPTOGRAPHY HOOKS OR EVEN JUST COMMUNICATING 273TECHNICAL DETAILS ABOUT CRYPTOGRAPHY SOFTWARE IS ILLEGAL IN SOME 274PARTS OF THE WORLD. SO, WHEN YOU IMPORT THIS PACKAGE TO YOUR 275COUNTRY, RE-DISTRIBUTE IT FROM THERE OR EVEN JUST EMAIL TECHNICAL 276SUGGESTIONS OR EVEN SOURCE PATCHES TO THE AUTHOR OR OTHER PEOPLE 277YOU ARE STRONGLY ADVISED TO PAY CLOSE ATTENTION TO ANY EXPORT/IMPORT 278AND/OR USE LAWS WHICH APPLY TO YOU. THE AUTHORS ARE NOT LIABLE FOR 279ANY VIOLATIONS YOU MAKE HERE. SO BE CAREFUL, IT IS YOUR RESPONSIBILITY. 280 281If you use OpenSSL then make sure you read their README file which 282contains information about patents etc. 283 284 285+-------------------+ 286| DATABASE ROUTINES | 287+-------------------+ 288 289IF YOU WANT TO RUN THE NEW BERKELEY DB SOFTWARE: **** DO NOT **** 290use the version that was on the Net2 tape -- it has a number of 291nefarious bugs that were bad enough when I got them; you shouldn't have 292to go through the same thing. Instead, get a new version via the web at 293http://www.sleepycat.com/. This software is highly recommended; it gets 294rid of several stupid limits, it's much faster, and the interface is 295nicer to animals and plants. If the Berkeley DB include files 296are installed in a location other than those which your compiler searches, 297you will need to provide that directory when building: 298 299 ./Build -I/path/to/include/directory 300 301If you are using Berkeley DB versions 1.85 or 1.86, you are *strongly* 302urged to upgrade to DB version 2 or later, available from 303http://www.sleepycat.com/. Berkeley DB versions 1.85 and 1.86 are known to 304be broken in various nasty ways (see http://www.sleepycat.com/db.185.html), 305and can cause sendmail to dump core. In addition, the newest versions of 306gcc and the Solaris compilers perform optimizations in those versions that 307may cause fairly random core dumps. 308 309If you have no choice but to use Berkeley DB 1.85 or 1.86, and you are 310using both Berkeley DB and files in the UNIX ndbm format, remove ndbm.h 311and ndbm.o from the DB library after building it. You should also apply 312all of the patches for DB 1.85 and 1.86 found at the Sleepycat web site 313(see http://www.sleepycat.com/db.185.html), as they fix some of the known 314problems. 315 316If you are using a version of Berkeley DB 2 previous to 2.3.15, and you 317are using both Berkeley DB and files in the UNIX ndbm format, remove dbm.o 318from the DB library after building it. No other changes are necessary. 319 320If you are using Berkeley DB version 2.3.15 or greater, no changes are 321necessary. 322 323The underlying database file formats changed between Berkeley DB versions 3241.85 and 1.86, again between DB 1.86 and version 2.0, and finally between 325DB 2.X and 3.X. If you are upgrading from one of those versions, you must 326recreate your database file(s). Do this by rebuilding all maps with 327makemap and rebuilding the alias file with newaliases. 328 329File locking using fcntl() does not interoperate with Berkeley DB 3305.x (and probably later). Use CDB, flock() (-DHASFLOCK), or an 331earlier Berkeley DB version. 332 333 334+--------------------+ 335| HOST NAME SERVICES | 336+--------------------+ 337 338If you are using NIS or /etc/hosts, it is critical that you 339list the long (fully qualified) name somewhere (preferably first) in 340the /etc/hosts file used to build the NIS database. For example, the 341line should read 342 343 128.32.149.68 mastodon.CS.Berkeley.EDU mastodon 344 345**** NOT **** 346 347 128.32.149.68 mastodon 348 349If you do not include the long name, sendmail will complain loudly 350about ``unable to qualify my own domain name (mastodon) -- using 351short name'' and conclude that your canonical name is the short 352version and use that in messages. The name "mastodon" doesn't mean 353much outside of Berkeley, and so this creates incorrect and unreplyable 354messages. 355 356 357+-------------+ 358| USE WITH MH | 359+-------------+ 360 361This version of sendmail notices and reports certain kinds of SMTP 362protocol violations that were ignored by older versions. If you 363are running MH you may wish to install the patch in contrib/mh.patch 364that will prevent these warning reports. This patch also works 365with the old version of sendmail, so it's safe to go ahead and 366install it. 367 368 369+----------------+ 370| USE WITH IDENT | 371+----------------+ 372 373Sendmail 8 supports the IDENT protocol, as defined by RFC 1413. 374Note that the RFC states a client should wait at least 30 seconds 375for a response. As of 8.10.0, the default Timeout.ident is 5 seconds 376as many sites have adopted the practice of dropping IDENT queries. 377This has lead to delays processing mail. 378 379 380+-------------------------+ 381| INTEROPERATION PROBLEMS | 382+-------------------------+ 383 384Microsoft Exchange Server 5.0 385 We have had a report that ``about 7% of messages from Sendmail 386 to Exchange were not being delivered with status messages of 387 "connection reset" and "I/O error".'' Upgrading Exchange from 388 Version 5.0 to Version 5.5 Service Pack 2 solved this problem. 389 390CommuniGate Pro 391 CommuniGate Pro 3.2.4 does not accept the AUTH= -parameter on 392 the MAIL FROM command if the client is not authenticated. Use 393 394 define(`confAUTH_OPTIONS', `A') 395 396 in .mc file if you have compiled sendmail with Cyrus SASL 397 and you communicate with CommuniGate Pro servers. 398 399 400+---------------------+ 401| DIRECTORY STRUCTURE | 402+---------------------+ 403 404The structure of this directory tree is: 405 406cf Source for sendmail configuration files. These are 407 different than what you've seen before. They are a 408 fairly dramatic rewrite, requiring the new sendmail 409 (since they use new features). 410contrib Some contributed tools to help with sendmail. THESE 411 ARE NOT SUPPORTED by sendmail -- contact the original 412 authors if you have problems. (This directory is not 413 on the 4.4BSD tape.) 414devtools Build environment. See devtools/README. 415doc Documentation. If you are getting source, read 416 op.me -- it's long, but worth it. 417editmap A program to edit and query maps that have been created 418 with makemap, e.g., adding and deleting entries. 419include Include files used by multiple programs in the distribution. 420libsmdb sendmail database library with support for Berkeley DB 1.X, 421 Berkeley DB 2.X, Berkeley DB 3.X, and NDBM. 422libsmutil sendmail utility library with functions used by different 423 programs. 424mail.local The source for the local delivery agent used for 4.4BSD. 425 THIS IS NOT PART OF SENDMAIL! and may not compile 426 everywhere, since it depends on some 4.4-isms. Warning: 427 it does mailbox locking differently than other systems. 428mailstats Statistics printing program. 429makemap A program that creates the keyed maps used by the $( ... $) 430 construct in sendmail. It is primitive but effective. 431 It takes a very simple input format, so you will probably 432 expect to preprocess must human-convenient formats 433 using sed scripts before this program will like them. 434 But it should be functionally complete. 435praliases A program to print the map version of the aliases file. 436rmail Source for rmail(8). This is used as a delivery 437 agent for for UUCP, and could presumably be used by 438 other non-socket oriented mailers. Older versions of 439 rmail are probably deficient. RMAIL IS NOT PART OF 440 SENDMAIL!!! The 4.4BSD source is included for you to 441 look at or try to port to your system. There is no 442 guarantee it will even compile on your operating system. 443smrsh The "sendmail restricted shell", which can be used as 444 a replacement for /bin/sh in the prog mailer to provide 445 increased security control. NOT PART OF SENDMAIL! 446sendmail Source for the sendmail program itself. 447test Some test scripts (currently only for compilation aids). 448vacation Source for the vacation program. NOT PART OF SENDMAIL! 449 450