1<!doctype html public "-//W3C//DTD HTML 4.01 Transitional//EN" 2 "http://www.w3.org/TR/html4/loose.dtd"> 3<html> <head> 4<meta http-equiv="Content-Type" content="text/html; charset=us-ascii"> 5<title> Postfix manual - postscreen(8) </title> 6</head> <body> <pre> 7POSTSCREEN(8) POSTSCREEN(8) 8 9<b>NAME</b> 10 postscreen - Postfix zombie blocker 11 12<b>SYNOPSIS</b> 13 <b>postscreen</b> [generic Postfix daemon options] 14 15<b>DESCRIPTION</b> 16 The Postfix <a href="postscreen.8.html"><b>postscreen</b>(8)</a> server performs triage on multi- 17 ple inbound SMTP connections at the same time. While a 18 single <a href="postscreen.8.html"><b>postscreen</b>(8)</a> process keeps spambots away from 19 Postfix SMTP server processes, more Postfix SMTP server 20 processes remain available for legitimate clients. 21 22 This program should not be used on SMTP ports that receive 23 mail from end-user clients (MUAs). In a typical deploy- 24 ment, <a href="postscreen.8.html"><b>postscreen</b>(8)</a> is used on the "port 25" service, 25 while MUA clients submit mail via the <b>submission</b> service. 26 27 <a href="postscreen.8.html"><b>postscreen</b>(8)</a> maintains a temporary whitelist for clients 28 that have passed a number of tests. When an SMTP client 29 IP address is whitelisted, <a href="postscreen.8.html"><b>postscreen</b>(8)</a> hands off the 30 connection immediately to a Postfix SMTP server process. 31 This minimizes the overhead for legitimate mail. 32 33 By default, <a href="postscreen.8.html"><b>postscreen</b>(8)</a> logs statistics and hands off 34 every connection to a Postfix SMTP server process, while 35 excluding clients in <a href="postconf.5.html#mynetworks">mynetworks</a> from all tests (primarily, 36 to avoid problems with non-standard SMTP implementations 37 in network appliances). This mode is useful for non- 38 destructive testing. 39 40 In a typical production setting, <a href="postscreen.8.html"><b>postscreen</b>(8)</a> is config- 41 ured to reject mail from clients that fail one or more 42 tests. <a href="postscreen.8.html"><b>postscreen</b>(8)</a> logs rejected mail with the client 43 address, helo, sender and recipient information. 44 45 <a href="postscreen.8.html"><b>postscreen</b>(8)</a> is not an SMTP proxy; this is intentional. 46 The purpose is to keep spambots away from Postfix SMTP 47 server processes, while minimizing overhead for legitimate 48 traffic. 49 50<b>SECURITY</b> 51 The <a href="postscreen.8.html"><b>postscreen</b>(8)</a> server is moderately security-sensitive. 52 It talks to untrusted clients on the network. The process 53 can be run chrooted at fixed low privilege. 54 55<b>STANDARDS</b> 56 <a href="http://tools.ietf.org/html/rfc821">RFC 821</a> (SMTP protocol) 57 <a href="http://tools.ietf.org/html/rfc1123">RFC 1123</a> (Host requirements) 58 <a href="http://tools.ietf.org/html/rfc1652">RFC 1652</a> (8bit-MIME transport) 59 <a href="http://tools.ietf.org/html/rfc1869">RFC 1869</a> (SMTP service extensions) 60 <a href="http://tools.ietf.org/html/rfc1870">RFC 1870</a> (Message Size Declaration) 61 <a href="http://tools.ietf.org/html/rfc1985">RFC 1985</a> (ETRN command) 62 <a href="http://tools.ietf.org/html/rfc2034">RFC 2034</a> (SMTP Enhanced Status Codes) 63 <a href="http://tools.ietf.org/html/rfc2821">RFC 2821</a> (SMTP protocol) 64 Not: <a href="http://tools.ietf.org/html/rfc2920">RFC 2920</a> (SMTP Pipelining) 65 <a href="http://tools.ietf.org/html/rfc3207">RFC 3207</a> (STARTTLS command) 66 <a href="http://tools.ietf.org/html/rfc3461">RFC 3461</a> (SMTP DSN Extension) 67 <a href="http://tools.ietf.org/html/rfc3463">RFC 3463</a> (Enhanced Status Codes) 68 <a href="http://tools.ietf.org/html/rfc5321">RFC 5321</a> (SMTP protocol, including multi-line 220 banners) 69 70<b>DIAGNOSTICS</b> 71 Problems and transactions are logged to <b>syslogd</b>(8). 72 73<b>BUGS</b> 74 The <a href="postscreen.8.html"><b>postscreen</b>(8)</a> built-in SMTP protocol engine currently 75 does not announce support for AUTH, XCLIENT or XFORWARD. 76 Support for AUTH may be added in the future. In the mean 77 time, if you need to make these services available on port 78 25, then do not enable the optional "after 220 server 79 greeting" tests, and do not use DNSBLs that reject traffic 80 from dial-up and residential networks. 81 82 The optional "after 220 server greeting" tests involve 83 <a href="postscreen.8.html"><b>postscreen</b>(8)</a>'s built-in SMTP protocol engine. When these 84 tests succeed, <a href="postscreen.8.html"><b>postscreen</b>(8)</a> adds the client to the tempo- 85 rary whitelist but it cannot not hand off the "live" con- 86 nection to a Postfix SMTP server process in the middle of 87 a session. Instead, <a href="postscreen.8.html"><b>postscreen</b>(8)</a> defers attempts to 88 deliver mail with a 4XX status, and waits for the client 89 to disconnect. The next time a good client connects, it 90 will be allowed to talk to a Postfix SMTP server process 91 to deliver mail. <a href="postscreen.8.html"><b>postscreen</b>(8)</a> mitigates the impact of 92 this limitation by giving such tests a long expiration 93 time. 94 95<b>CONFIGURATION PARAMETERS</b> 96 Changes to <a href="postconf.5.html">main.cf</a> are not picked up automatically, as 97 <a href="postscreen.8.html"><b>postscreen</b>(8)</a> processes may run for several hours. Use 98 the command "postfix reload" after a configuration change. 99 100 The text below provides only a parameter summary. See 101 <a href="postconf.5.html"><b>postconf</b>(5)</a> for more details including examples. 102 103 NOTE: Some <a href="postscreen.8.html"><b>postscreen</b>(8)</a> parameters implement stress- 104 dependent behavior. This is supported only when the 105 default parameter value is stress-dependent (that is, it 106 looks like ${stress?X}${stress:Y}, or it is the $<i>name</i> of 107 an smtpd parameter with a stress-dependent default). 108 Other parameters always evaluate as if the <b>stress</b> parame- 109 ter value is the empty string. 110 111<b>COMPATIBILITY CONTROLS</b> 112 <b><a href="postconf.5.html#postscreen_command_filter">postscreen_command_filter</a> ($<a href="postconf.5.html#smtpd_command_filter">smtpd_command_filter</a>)</b> 113 A mechanism to transform commands from remote SMTP 114 clients. 115 116 <b><a href="postconf.5.html#postscreen_discard_ehlo_keyword_address_maps">postscreen_discard_ehlo_keyword_address_maps</a> ($<a href="postconf.5.html#smtpd_discard_ehlo_keyword_address_maps">smtpd_dis</a>-</b> 117 <b><a href="postconf.5.html#smtpd_discard_ehlo_keyword_address_maps">card_ehlo_keyword_address_maps</a>)</b> 118 Lookup tables, indexed by the remote SMTP client 119 address, with case insensitive lists of EHLO key- 120 words (pipelining, starttls, auth, etc.) that the 121 <a href="postscreen.8.html"><b>postscreen</b>(8)</a> server will not send in the EHLO 122 response to a remote SMTP client. 123 124 <b><a href="postconf.5.html#postscreen_discard_ehlo_keywords">postscreen_discard_ehlo_keywords</a> ($<a href="postconf.5.html#smtpd_discard_ehlo_keywords">smtpd_discard_ehlo_key</a>-</b> 125 <b><a href="postconf.5.html#smtpd_discard_ehlo_keywords">words</a>)</b> 126 A case insensitive list of EHLO keywords (pipelin- 127 ing, starttls, auth, etc.) that the <a href="postscreen.8.html"><b>postscreen</b>(8)</a> 128 server will not send in the EHLO response to a 129 remote SMTP client. 130 131<b>TROUBLE SHOOTING CONTROLS</b> 132 <b><a href="postconf.5.html#postscreen_expansion_filter">postscreen_expansion_filter</a> (see 'postconf -d' output)</b> 133 List of characters that are permitted in 134 <a href="postconf.5.html#postscreen_reject_footer">postscreen_reject_footer</a> attribute expansions. 135 136 <b><a href="postconf.5.html#postscreen_reject_footer">postscreen_reject_footer</a> ($<a href="postconf.5.html#smtpd_reject_footer">smtpd_reject_footer</a>)</b> 137 Optional information that is appended after a 4XX 138 or 5XX server response. 139 140 <b><a href="postconf.5.html#soft_bounce">soft_bounce</a> (no)</b> 141 Safety net to keep mail queued that would otherwise 142 be returned to the sender. 143 144<b>PERMANENT WHITE/BLACKLIST TEST</b> 145 This test is executed immediately after a remote SMTP 146 client connects. If a client is permanently whitelisted, 147 the client will be handed off immediately to a Postfix 148 SMTP server process. 149 150 <b><a href="postconf.5.html#postscreen_access_list">postscreen_access_list</a> (<a href="postconf.5.html#permit_mynetworks">permit_mynetworks</a>)</b> 151 Permanent white/blacklist for remote SMTP client IP 152 addresses. 153 154 <b><a href="postconf.5.html#postscreen_blacklist_action">postscreen_blacklist_action</a> (ignore)</b> 155 The action that <a href="postscreen.8.html"><b>postscreen</b>(8)</a> takes when an SMTP 156 client is permanently blacklisted with the 157 <a href="postconf.5.html#postscreen_access_list">postscreen_access_list</a> parameter. 158 159<b>BEFORE-GREETING TESTS</b> 160 These tests are executed before the remote SMTP client 161 receives the "220 servername" greeting. If no tests remain 162 after the successful completion of this phase, the client 163 will be handed off immediately to a Postfix SMTP server 164 process. 165 166 <b><a href="postconf.5.html#dnsblog_service_name">dnsblog_service_name</a> (dnsblog)</b> 167 The name of the <a href="dnsblog.8.html"><b>dnsblog</b>(8)</a> service entry in mas- 168 ter.cf. 169 170 <b><a href="postconf.5.html#postscreen_dnsbl_action">postscreen_dnsbl_action</a> (ignore)</b> 171 The action that <a href="postscreen.8.html"><b>postscreen</b>(8)</a> takes when an SMTP 172 client's combined DNSBL score is equal to or 173 greater than a threshold (as defined with the 174 <a href="postconf.5.html#postscreen_dnsbl_sites">postscreen_dnsbl_sites</a> and <a href="postconf.5.html#postscreen_dnsbl_threshold">postscreen_dnsbl_thresh</a>- 175 <a href="postconf.5.html#postscreen_dnsbl_threshold">old</a> parameters). 176 177 <b><a href="postconf.5.html#postscreen_dnsbl_reply_map">postscreen_dnsbl_reply_map</a> (empty)</b> 178 A mapping from actual DNSBL domain name which 179 includes a secret password, to the DNSBL domain 180 name that postscreen will reply with when it 181 rejects mail. 182 183 <b><a href="postconf.5.html#postscreen_dnsbl_sites">postscreen_dnsbl_sites</a> (empty)</b> 184 Optional list of DNS white/blacklist domains, fil- 185 ters and weight factors. 186 187 <b><a href="postconf.5.html#postscreen_dnsbl_threshold">postscreen_dnsbl_threshold</a> (1)</b> 188 The inclusive lower bound for blocking an SMTP 189 client, based on its combined DNSBL score as 190 defined with the <a href="postconf.5.html#postscreen_dnsbl_sites">postscreen_dnsbl_sites</a> parameter. 191 192 <b><a href="postconf.5.html#postscreen_greet_action">postscreen_greet_action</a> (ignore)</b> 193 The action that <a href="postscreen.8.html"><b>postscreen</b>(8)</a> takes when an SMTP 194 client speaks before its turn within the time spec- 195 ified with the <a href="postconf.5.html#postscreen_greet_wait">postscreen_greet_wait</a> parameter. 196 197 <b><a href="postconf.5.html#postscreen_greet_banner">postscreen_greet_banner</a> ($<a href="postconf.5.html#smtpd_banner">smtpd_banner</a>)</b> 198 The <i>text</i> in the optional "220-<i>text</i>..." server 199 response that <a href="postscreen.8.html"><b>postscreen</b>(8)</a> sends ahead of the real 200 Postfix SMTP server's "220 text..." response, in an 201 attempt to confuse bad SMTP clients so that they 202 speak before their turn (pre-greet). 203 204 <b><a href="postconf.5.html#postscreen_greet_wait">postscreen_greet_wait</a> (${stress?2}${stress:6}s)</b> 205 The amount of time that <a href="postscreen.8.html"><b>postscreen</b>(8)</a> will wait for 206 an SMTP client to send a command before its turn, 207 and for DNS blocklist lookup results to arrive 208 (default: up to 2 seconds under stress, up to 6 209 seconds otherwise). 210 211 <b><a href="postconf.5.html#smtpd_service_name">smtpd_service_name</a> (smtpd)</b> 212 The internal service that <a href="postscreen.8.html"><b>postscreen</b>(8)</a> forwards 213 allowed connections to. 214 215<b>AFTER-GREETING TESTS</b> 216 These tests are executed after the remote SMTP client 217 receives the "220 servername" greeting. If a client passes 218 all tests during this phase, it will receive a 4XX 219 response to RCPT TO commands until the client hangs up. 220 After this, the client will be allowed to talk directly to 221 a Postfix SMTP server process. 222 223 <b><a href="postconf.5.html#postscreen_bare_newline_action">postscreen_bare_newline_action</a> (ignore)</b> 224 The action that <a href="postscreen.8.html"><b>postscreen</b>(8)</a> takes when an SMTP 225 client sends a bare newline character, that is, a 226 newline not preceded by carriage return. 227 228 <b><a href="postconf.5.html#postscreen_bare_newline_enable">postscreen_bare_newline_enable</a> (no)</b> 229 Enable "bare newline" SMTP protocol tests in the 230 <a href="postscreen.8.html"><b>postscreen</b>(8)</a> server. 231 232 <b><a href="postconf.5.html#postscreen_disable_vrfy_command">postscreen_disable_vrfy_command</a> ($<a href="postconf.5.html#disable_vrfy_command">disable_vrfy_command</a>)</b> 233 Disable the SMTP VRFY command in the <a href="postscreen.8.html"><b>postscreen</b>(8)</a> 234 daemon. 235 236 <b><a href="postconf.5.html#postscreen_forbidden_commands">postscreen_forbidden_commands</a> ($<a href="postconf.5.html#smtpd_forbidden_commands">smtpd_forbidden_commands</a>)</b> 237 List of commands that the <a href="postscreen.8.html"><b>postscreen</b>(8)</a> server con- 238 siders in violation of the SMTP protocol. 239 240 <b><a href="postconf.5.html#postscreen_helo_required">postscreen_helo_required</a> ($<a href="postconf.5.html#smtpd_helo_required">smtpd_helo_required</a>)</b> 241 Require that a remote SMTP client sends HELO or 242 EHLO before commencing a MAIL transaction. 243 244 <b><a href="postconf.5.html#postscreen_non_smtp_command_action">postscreen_non_smtp_command_action</a> (drop)</b> 245 The action that <a href="postscreen.8.html"><b>postscreen</b>(8)</a> takes when an SMTP 246 client sends non-SMTP commands as specified with 247 the <a href="postconf.5.html#postscreen_forbidden_commands">postscreen_forbidden_commands</a> parameter. 248 249 <b><a href="postconf.5.html#postscreen_non_smtp_command_enable">postscreen_non_smtp_command_enable</a> (no)</b> 250 Enable "non-SMTP command" tests in the 251 <a href="postscreen.8.html"><b>postscreen</b>(8)</a> server. 252 253 <b><a href="postconf.5.html#postscreen_pipelining_action">postscreen_pipelining_action</a> (enforce)</b> 254 The action that <a href="postscreen.8.html"><b>postscreen</b>(8)</a> takes when an SMTP 255 client sends multiple commands instead of sending 256 one command and waiting for the server to respond. 257 258 <b><a href="postconf.5.html#postscreen_pipelining_enable">postscreen_pipelining_enable</a> (no)</b> 259 Enable "pipelining" SMTP protocol tests in the 260 <a href="postscreen.8.html"><b>postscreen</b>(8)</a> server. 261 262<b>CACHE CONTROLS</b> 263 <b><a href="postconf.5.html#postscreen_cache_cleanup_interval">postscreen_cache_cleanup_interval</a> (12h)</b> 264 The amount of time between <a href="postscreen.8.html"><b>postscreen</b>(8)</a> cache 265 cleanup runs. 266 267 <b><a href="postconf.5.html#postscreen_cache_map">postscreen_cache_map</a> (btree:$data_direc-</b> 268 <b>tory/postscreen_cache)</b> 269 Persistent storage for the <a href="postscreen.8.html"><b>postscreen</b>(8)</a> server 270 decisions. 271 272 <b><a href="postconf.5.html#postscreen_cache_retention_time">postscreen_cache_retention_time</a> (7d)</b> 273 The amount of time that <a href="postscreen.8.html"><b>postscreen</b>(8)</a> will cache an 274 expired temporary whitelist entry before it is 275 removed. 276 277 <b><a href="postconf.5.html#postscreen_bare_newline_ttl">postscreen_bare_newline_ttl</a> (30d)</b> 278 The amount of time that <a href="postscreen.8.html"><b>postscreen</b>(8)</a> will use the 279 result from a successful "bare newline" SMTP proto- 280 col test. 281 282 <b><a href="postconf.5.html#postscreen_dnsbl_ttl">postscreen_dnsbl_ttl</a> (1h)</b> 283 The amount of time that <a href="postscreen.8.html"><b>postscreen</b>(8)</a> will use the 284 result from a successful DNS blocklist test. 285 286 <b><a href="postconf.5.html#postscreen_greet_ttl">postscreen_greet_ttl</a> (1d)</b> 287 The amount of time that <a href="postscreen.8.html"><b>postscreen</b>(8)</a> will use the 288 result from a successful PREGREET test. 289 290 <b><a href="postconf.5.html#postscreen_non_smtp_command_ttl">postscreen_non_smtp_command_ttl</a> (30d)</b> 291 The amount of time that <a href="postscreen.8.html"><b>postscreen</b>(8)</a> will use the 292 result from a successful "non_smtp_command" SMTP 293 protocol test. 294 295 <b><a href="postconf.5.html#postscreen_pipelining_ttl">postscreen_pipelining_ttl</a> (30d)</b> 296 The amount of time that <a href="postscreen.8.html"><b>postscreen</b>(8)</a> will use the 297 result from a successful "pipelining" SMTP protocol 298 test. 299 300<b>RESOURCE CONTROLS</b> 301 <b><a href="postconf.5.html#line_length_limit">line_length_limit</a> (2048)</b> 302 Upon input, long lines are chopped up into pieces 303 of at most this length; upon delivery, long lines 304 are reconstructed. 305 306 <b><a href="postconf.5.html#postscreen_client_connection_count_limit">postscreen_client_connection_count_limit</a></b> 307 <b>($<a href="postconf.5.html#smtpd_client_connection_count_limit">smtpd_client_connection_count_limit</a>)</b> 308 How many simultaneous connections any client is 309 allowed to have with the <a href="postscreen.8.html"><b>postscreen</b>(8)</a> daemon. 310 311 <b><a href="postconf.5.html#postscreen_command_count_limit">postscreen_command_count_limit</a> (20)</b> 312 The limit on the total number of commands per SMTP 313 session for <a href="postscreen.8.html"><b>postscreen</b>(8)</a>'s built-in SMTP protocol 314 engine. 315 316 <b><a href="postconf.5.html#postscreen_command_time_limit">postscreen_command_time_limit</a> (${stress?10}${stress:300}s)</b> 317 The time limit to read an entire command line with 318 <a href="postscreen.8.html"><b>postscreen</b>(8)</a>'s built-in SMTP protocol engine. 319 320 <b><a href="postconf.5.html#postscreen_post_queue_limit">postscreen_post_queue_limit</a> ($<a href="postconf.5.html#default_process_limit">default_process_limit</a>)</b> 321 The number of clients that can be waiting for ser- 322 vice from a real SMTP server process. 323 324 <b><a href="postconf.5.html#postscreen_pre_queue_limit">postscreen_pre_queue_limit</a> ($<a href="postconf.5.html#default_process_limit">default_process_limit</a>)</b> 325 The number of non-whitelisted clients that can be 326 waiting for a decision whether they will receive 327 service from a real SMTP server process. 328 329 <b><a href="postconf.5.html#postscreen_watchdog_timeout">postscreen_watchdog_timeout</a> (10s)</b> 330 How much time a <a href="postscreen.8.html"><b>postscreen</b>(8)</a> process may take to 331 respond to an SMTP client command or to perform a 332 cache operation before it is terminated by a built- 333 in watchdog timer. 334 335<b>STARTTLS CONTROLS</b> 336 <b><a href="postconf.5.html#postscreen_tls_security_level">postscreen_tls_security_level</a> ($<a href="postconf.5.html#smtpd_tls_security_level">smtpd_tls_security_level</a>)</b> 337 The SMTP TLS security level for the <a href="postscreen.8.html"><b>postscreen</b>(8)</a> 338 server; when a non-empty value is specified, this 339 overrides the obsolete parameters 340 <a href="postconf.5.html#postscreen_use_tls">postscreen_use_tls</a> and <a href="postconf.5.html#postscreen_enforce_tls">postscreen_enforce_tls</a>. 341 342 <b><a href="postconf.5.html#tlsproxy_service_name">tlsproxy_service_name</a> (tlsproxy)</b> 343 The name of the <a href="tlsproxy.8.html"><b>tlsproxy</b>(8)</a> service entry in mas- 344 ter.cf. 345 346<b>OBSOLETE STARTTLS SUPPORT CONTROLS</b> 347 These parameters are supported for compatibility with 348 <a href="smtpd.8.html"><b>smtpd</b>(8)</a> legacy parameters. 349 350 <b><a href="postconf.5.html#postscreen_use_tls">postscreen_use_tls</a> ($<a href="postconf.5.html#smtpd_use_tls">smtpd_use_tls</a>)</b> 351 Opportunistic TLS: announce STARTTLS support to 352 SMTP clients, but do not require that clients use 353 TLS encryption. 354 355 <b><a href="postconf.5.html#postscreen_enforce_tls">postscreen_enforce_tls</a> ($<a href="postconf.5.html#smtpd_enforce_tls">smtpd_enforce_tls</a>)</b> 356 Mandatory TLS: announce STARTTLS support to SMTP 357 clients, and require that clients use TLS encryp- 358 tion. 359 360<b>MISCELLANEOUS CONTROLS</b> 361 <b><a href="postconf.5.html#config_directory">config_directory</a> (see 'postconf -d' output)</b> 362 The default location of the Postfix <a href="postconf.5.html">main.cf</a> and 363 <a href="master.5.html">master.cf</a> configuration files. 364 365 <b><a href="postconf.5.html#delay_logging_resolution_limit">delay_logging_resolution_limit</a> (2)</b> 366 The maximal number of digits after the decimal 367 point when logging sub-second delay values. 368 369 <b><a href="postconf.5.html#command_directory">command_directory</a> (see 'postconf -d' output)</b> 370 The location of all postfix administrative com- 371 mands. 372 373 <b><a href="postconf.5.html#max_idle">max_idle</a> (100s)</b> 374 The maximum amount of time that an idle Postfix 375 daemon process waits for an incoming connection 376 before terminating voluntarily. 377 378 <b><a href="postconf.5.html#process_id">process_id</a> (read-only)</b> 379 The process ID of a Postfix command or daemon 380 process. 381 382 <b><a href="postconf.5.html#process_name">process_name</a> (read-only)</b> 383 The process name of a Postfix command or daemon 384 process. 385 386 <b><a href="postconf.5.html#syslog_facility">syslog_facility</a> (mail)</b> 387 The syslog facility of Postfix logging. 388 389 <b><a href="postconf.5.html#syslog_name">syslog_name</a> (see 'postconf -d' output)</b> 390 The mail system name that is prepended to the 391 process name in syslog records, so that "smtpd" 392 becomes, for example, "postfix/smtpd". 393 394<b>SEE ALSO</b> 395 <a href="smtpd.8.html">smtpd(8)</a>, Postfix SMTP server 396 <a href="tlsproxy.8.html">tlsproxy(8)</a>, Postfix TLS proxy server 397 <a href="dnsblog.8.html">dnsblog(8)</a>, DNS black/whitelist logger 398 syslogd(8), system logging 399 400<b>README FILES</b> 401 <a href="POSTSCREEN_README.html">POSTSCREEN_README</a>, Postfix Postscreen Howto 402 403<b>LICENSE</b> 404 The Secure Mailer license must be distributed with this 405 software. 406 407<b>HISTORY</b> 408 This service was introduced with Postfix version 2.8. 409 410 Many ideas in <a href="postscreen.8.html"><b>postscreen</b>(8)</a> were explored in earlier work 411 by Michael Tokarev, in OpenBSD spamd, and in MailChannels 412 Traffic Control. 413 414<b>AUTHOR(S)</b> 415 Wietse Venema 416 IBM T.J. Watson Research 417 P.O. Box 704 418 Yorktown Heights, NY 10598, USA 419 420 POSTSCREEN(8) 421</pre> </body> </html> 422