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7bafa7d9 TK |
1 | From time to time, experimental features may be added to Exim. |
2 | While a feature is experimental, there will be a build-time | |
3 | option whose name starts "EXPERIMENTAL_" that must be set in | |
4 | order to include the feature. This file contains information | |
5 | about experimenatal features, all of which are unstable and | |
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6 | liable to incompatibile change. |
7 | ||
8 | ||
0b23848a | 9 | Brightmail AntiSpam (BMI) suppport |
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10 | -------------------------------------------------------------- |
11 | ||
12 | Brightmail AntiSpam is a commercial package. Please see | |
13 | http://www.brightmail.com for more information on | |
14 | the product. For the sake of clarity, we'll refer to it as | |
15 | "BMI" from now on. | |
16 | ||
17 | ||
18 | 0) BMI concept and implementation overview | |
19 | ||
20 | In contrast to how spam-scanning with SpamAssassin is | |
21 | implemented in exiscan-acl, BMI is more suited for per | |
22 | -recipient scanning of messages. However, each messages is | |
23 | scanned only once, but multiple "verdicts" for multiple | |
24 | recipients can be returned from the BMI server. The exiscan | |
25 | implementation passes the message to the BMI server just | |
26 | before accepting it. It then adds the retrieved verdicts to | |
27 | the messages header file in the spool. These verdicts can then | |
28 | be queried in routers, where operation is per-recipient | |
29 | instead of per-message. To use BMI, you need to take the | |
30 | following steps: | |
31 | ||
32 | 1) Compile Exim with BMI support | |
3ec3e3bb | 33 | 2) Set up main BMI options (top section of Exim config file) |
ee161e8f PH |
34 | 3) Set up ACL control statement (ACL section of the config |
35 | file) | |
36 | 4) Set up your routers to use BMI verdicts (routers section | |
37 | of the config file). | |
38 | 5) (Optional) Set up per-recipient opt-in information. | |
39 | ||
8ff3788c | 40 | These four steps are explained in more details below. |
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41 | |
42 | 1) Adding support for BMI at compile time | |
43 | ||
44 | To compile with BMI support, you need to link Exim against | |
45 | the Brighmail client SDK, consisting of a library | |
46 | (libbmiclient_single.so) and a header file (bmi_api.h). | |
47 | You'll also need to explicitly set a flag in the Makefile to | |
48 | include BMI support in the Exim binary. Both can be achieved | |
49 | with these lines in Local/Makefile: | |
50 | ||
51 | EXPERIMENTAL_BRIGHTMAIL=yes | |
47bbda99 | 52 | CFLAGS=-I/path/to/the/dir/with/the/includefile |
ee161e8f | 53 | EXTRALIBS_EXIM=-L/path/to/the/dir/with/the/library -lbmiclient_single |
8ff3788c | 54 | |
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55 | If you use other CFLAGS or EXTRALIBS_EXIM settings then |
56 | merge the content of these lines with them. | |
57 | ||
7c0c8547 | 58 | Note for BMI6.x users: You'll also have to add -lxml2_single |
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59 | to the EXTRALIBS_EXIM line. Users of 5.5x do not need to do |
60 | this. | |
8ff3788c | 61 | |
ee161e8f PH |
62 | You should also include the location of |
63 | libbmiclient_single.so in your dynamic linker configuration | |
64 | file (usually /etc/ld.so.conf) and run "ldconfig" | |
65 | afterwards, or else the produced Exim binary will not be | |
66 | able to find the library file. | |
67 | ||
68 | ||
3ec3e3bb | 69 | 2) Setting up BMI support in the Exim main configuration |
ee161e8f | 70 | |
3ec3e3bb | 71 | To enable BMI support in the main Exim configuration, you |
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72 | should set the path to the main BMI configuration file with |
73 | the "bmi_config_file" option, like this: | |
8ff3788c | 74 | |
ee161e8f | 75 | bmi_config_file = /opt/brightmail/etc/brightmail.cfg |
8ff3788c | 76 | |
3ec3e3bb | 77 | This must go into section 1 of Exim's configuration file (You |
ee161e8f PH |
78 | can put it right on top). If you omit this option, it |
79 | defaults to /opt/brightmail/etc/brightmail.cfg. | |
80 | ||
81 | Note for BMI6.x users: This file is in XML format in V6.xx | |
82 | and its name is /opt/brightmail/etc/bmiconfig.xml. So BMI | |
83 | 6.x users MUST set the bmi_config_file option. | |
8ff3788c | 84 | |
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85 | |
86 | 3) Set up ACL control statement | |
87 | ||
88 | To optimize performance, it makes sense only to process | |
89 | messages coming from remote, untrusted sources with the BMI | |
90 | server. To set up a messages for processing by the BMI | |
91 | server, you MUST set the "bmi_run" control statement in any | |
92 | ACL for an incoming message. You will typically do this in | |
93 | an "accept" block in the "acl_check_rcpt" ACL. You should | |
94 | use the "accept" block(s) that accept messages from remote | |
95 | servers for your own domain(s). Here is an example that uses | |
3ec3e3bb | 96 | the "accept" blocks from Exim's default configuration file: |
8ff3788c | 97 | |
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98 | |
99 | accept domains = +local_domains | |
100 | endpass | |
101 | verify = recipient | |
102 | control = bmi_run | |
103 | ||
104 | accept domains = +relay_to_domains | |
105 | endpass | |
106 | verify = recipient | |
107 | control = bmi_run | |
8ff3788c | 108 | |
ee161e8f PH |
109 | If bmi_run is not set in any ACL during reception of the |
110 | message, it will NOT be passed to the BMI server. | |
111 | ||
112 | ||
113 | 4) Setting up routers to use BMI verdicts | |
114 | ||
115 | When a message has been run through the BMI server, one or | |
116 | more "verdicts" are present. Different recipients can have | |
117 | different verdicts. Each recipient is treated individually | |
118 | during routing, so you can query the verdicts by recipient | |
3ec3e3bb | 119 | at that stage. From Exim's view, a verdict can have the |
ee161e8f | 120 | following outcomes: |
8ff3788c | 121 | |
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122 | o deliver the message normally |
123 | o deliver the message to an alternate location | |
124 | o do not deliver the message | |
8ff3788c | 125 | |
ee161e8f PH |
126 | To query the verdict for a recipient, the implementation |
127 | offers the following tools: | |
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128 | |
129 | ||
ee161e8f PH |
130 | - Boolean router preconditions. These can be used in any |
131 | router. For a simple implementation of BMI, these may be | |
132 | all that you need. The following preconditions are | |
133 | available: | |
8ff3788c | 134 | |
ee161e8f | 135 | o bmi_deliver_default |
8ff3788c | 136 | |
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137 | This precondition is TRUE if the verdict for the |
138 | recipient is to deliver the message normally. If the | |
139 | message has not been processed by the BMI server, this | |
140 | variable defaults to TRUE. | |
8ff3788c | 141 | |
ee161e8f | 142 | o bmi_deliver_alternate |
8ff3788c | 143 | |
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144 | This precondition is TRUE if the verdict for the |
145 | recipient is to deliver the message to an alternate | |
146 | location. You can get the location string from the | |
147 | $bmi_alt_location expansion variable if you need it. See | |
148 | further below. If the message has not been processed by | |
149 | the BMI server, this variable defaults to FALSE. | |
8ff3788c | 150 | |
ee161e8f | 151 | o bmi_dont_deliver |
8ff3788c | 152 | |
ee161e8f PH |
153 | This precondition is TRUE if the verdict for the |
154 | recipient is NOT to deliver the message to the | |
155 | recipient. You will typically use this precondition in a | |
156 | top-level blackhole router, like this: | |
8ff3788c | 157 | |
ee161e8f PH |
158 | # don't deliver messages handled by the BMI server |
159 | bmi_blackhole: | |
160 | driver = redirect | |
161 | bmi_dont_deliver | |
162 | data = :blackhole: | |
8ff3788c | 163 | |
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164 | This router should be on top of all others, so messages |
165 | that should not be delivered do not reach other routers | |
166 | at all. If the message has not been processed by | |
167 | the BMI server, this variable defaults to FALSE. | |
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168 | |
169 | ||
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170 | - A list router precondition to query if rules "fired" on |
171 | the message for the recipient. Its name is "bmi_rule". You | |
172 | use it by passing it a colon-separated list of rule | |
173 | numbers. You can use this condition to route messages that | |
174 | matched specific rules. Here is an example: | |
8ff3788c | 175 | |
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176 | # special router for BMI rule #5, #8 and #11 |
177 | bmi_rule_redirect: | |
178 | driver = redirect | |
179 | bmi_rule = 5:8:11 | |
180 | data = postmaster@mydomain.com | |
8ff3788c TK |
181 | |
182 | ||
ee161e8f PH |
183 | - Expansion variables. Several expansion variables are set |
184 | during routing. You can use them in custom router | |
185 | conditions, for example. The following variables are | |
186 | available: | |
8ff3788c | 187 | |
ee161e8f | 188 | o $bmi_base64_verdict |
8ff3788c | 189 | |
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190 | This variable will contain the BASE64 encoded verdict |
191 | for the recipient being routed. You can use it to add a | |
192 | header to messages for tracking purposes, for example: | |
8ff3788c | 193 | |
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194 | localuser: |
195 | driver = accept | |
196 | check_local_user | |
197 | headers_add = X-Brightmail-Verdict: $bmi_base64_verdict | |
198 | transport = local_delivery | |
8ff3788c | 199 | |
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200 | If there is no verdict available for the recipient being |
201 | routed, this variable contains the empty string. | |
8ff3788c | 202 | |
ee161e8f | 203 | o $bmi_base64_tracker_verdict |
8ff3788c | 204 | |
ee161e8f PH |
205 | This variable will contain a BASE64 encoded subset of |
206 | the verdict information concerning the "rules" that | |
207 | fired on the message. You can add this string to a | |
208 | header, commonly named "X-Brightmail-Tracker". Example: | |
8ff3788c | 209 | |
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210 | localuser: |
211 | driver = accept | |
212 | check_local_user | |
213 | headers_add = X-Brightmail-Tracker: $bmi_base64_tracker_verdict | |
214 | transport = local_delivery | |
8ff3788c | 215 | |
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216 | If there is no verdict available for the recipient being |
217 | routed, this variable contains the empty string. | |
8ff3788c | 218 | |
ee161e8f | 219 | o $bmi_alt_location |
8ff3788c | 220 | |
ee161e8f PH |
221 | If the verdict is to redirect the message to an |
222 | alternate location, this variable will contain the | |
223 | alternate location string returned by the BMI server. In | |
224 | its default configuration, this is a header-like string | |
225 | that can be added to the message with "headers_add". If | |
226 | there is no verdict available for the recipient being | |
227 | routed, or if the message is to be delivered normally, | |
228 | this variable contains the empty string. | |
8ff3788c | 229 | |
ee161e8f | 230 | o $bmi_deliver |
8ff3788c | 231 | |
ee161e8f PH |
232 | This is an additional integer variable that can be used |
233 | to query if the message should be delivered at all. You | |
234 | should use router preconditions instead if possible. | |
8ff3788c | 235 | |
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236 | $bmi_deliver is '0': the message should NOT be delivered. |
237 | $bmi_deliver is '1': the message should be delivered. | |
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238 | |
239 | ||
ee161e8f PH |
240 | IMPORTANT NOTE: Verdict inheritance. |
241 | The message is passed to the BMI server during message | |
242 | reception, using the target addresses from the RCPT TO: | |
243 | commands in the SMTP transaction. If recipients get expanded | |
244 | or re-written (for example by aliasing), the new address(es) | |
245 | inherit the verdict from the original address. This means | |
246 | that verdicts also apply to all "child" addresses generated | |
247 | from top-level addresses that were sent to the BMI server. | |
8ff3788c TK |
248 | |
249 | ||
ee161e8f PH |
250 | 5) Using per-recipient opt-in information (Optional) |
251 | ||
252 | The BMI server features multiple scanning "profiles" for | |
253 | individual recipients. These are usually stored in a LDAP | |
254 | server and are queried by the BMI server itself. However, | |
255 | you can also pass opt-in data for each recipient from the | |
256 | MTA to the BMI server. This is particularly useful if you | |
3ec3e3bb | 257 | already look up recipient data in Exim anyway (which can |
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258 | also be stored in a SQL database or other source). This |
259 | implementation enables you to pass opt-in data to the BMI | |
260 | server in the RCPT ACL. This works by setting the | |
261 | 'bmi_optin' modifier in a block of that ACL. If should be | |
262 | set to a list of comma-separated strings that identify the | |
263 | features which the BMI server should use for that particular | |
264 | recipient. Ideally, you would use the 'bmi_optin' modifier | |
265 | in the same ACL block where you set the 'bmi_run' control | |
266 | flag. Here is an example that will pull opt-in data for each | |
267 | recipient from a flat file called | |
268 | '/etc/exim/bmi_optin_data'. | |
8ff3788c | 269 | |
ee161e8f | 270 | The file format: |
8ff3788c | 271 | |
ee161e8f PH |
272 | user1@mydomain.com: <OPTIN STRING1>:<OPTIN STRING2> |
273 | user2@thatdomain.com: <OPTIN STRING3> | |
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274 | |
275 | ||
ee161e8f | 276 | The example: |
8ff3788c | 277 | |
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278 | accept domains = +relay_to_domains |
279 | endpass | |
280 | verify = recipient | |
281 | bmi_optin = ${lookup{$local_part@$domain}lsearch{/etc/exim/bmi_optin_data}} | |
8ff3788c TK |
282 | control = bmi_run |
283 | ||
ee161e8f | 284 | Of course, you can also use any other lookup method that |
3ec3e3bb | 285 | Exim supports, including LDAP, Postgres, MySQL, Oracle etc., |
ee161e8f PH |
286 | as long as the result is a list of colon-separated opt-in |
287 | strings. | |
8ff3788c | 288 | |
ee161e8f PH |
289 | For a list of available opt-in strings, please contact your |
290 | Brightmail representative. | |
ee161e8f | 291 | |
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292 | |
293 | ||
294 | ||
0b23848a | 295 | Sender Policy Framework (SPF) support |
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296 | -------------------------------------------------------------- |
297 | ||
f413481d | 298 | To learn more about SPF, visit http://www.openspf.org. This |
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299 | document does not explain the SPF fundamentals, you should |
300 | read and understand the implications of deploying SPF on your | |
301 | system before doing so. | |
302 | ||
8ff3788c | 303 | SPF support is added via the libspf2 library. Visit |
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304 | |
305 | http://www.libspf2.org/ | |
8ff3788c | 306 | |
ee161e8f PH |
307 | to obtain a copy, then compile and install it. By default, |
308 | this will put headers in /usr/local/include and the static | |
309 | library in /usr/local/lib. | |
310 | ||
3ec3e3bb | 311 | To compile Exim with SPF support, set these additional flags in |
ee161e8f PH |
312 | Local/Makefile: |
313 | ||
314 | EXPERIMENTAL_SPF=yes | |
315 | CFLAGS=-DSPF -I/usr/local/include | |
316 | EXTRALIBS_EXIM=-L/usr/local/lib -lspf2 | |
317 | ||
318 | This assumes that the libspf2 files are installed in | |
319 | their default locations. | |
320 | ||
321 | You can now run SPF checks in incoming SMTP by using the "spf" | |
322 | ACL condition in either the MAIL, RCPT or DATA ACLs. When | |
323 | using it in the RCPT ACL, you can make the checks dependend on | |
324 | the RCPT address (or domain), so you can check SPF records | |
325 | only for certain target domains. This gives you the | |
326 | possibility to opt-out certain customers that do not want | |
327 | their mail to be subject to SPF checking. | |
328 | ||
329 | The spf condition takes a list of strings on its right-hand | |
330 | side. These strings describe the outcome of the SPF check for | |
331 | which the spf condition should succeed. Valid strings are: | |
332 | ||
333 | o pass The SPF check passed, the sending host | |
334 | is positively verified by SPF. | |
335 | o fail The SPF check failed, the sending host | |
336 | is NOT allowed to send mail for the domain | |
337 | in the envelope-from address. | |
338 | o softfail The SPF check failed, but the queried | |
339 | domain can't absolutely confirm that this | |
340 | is a forgery. | |
341 | o none The queried domain does not publish SPF | |
342 | records. | |
343 | o neutral The SPF check returned a "neutral" state. | |
344 | This means the queried domain has published | |
345 | a SPF record, but wants to allow outside | |
346 | servers to send mail under its domain as well. | |
347 | o err_perm This indicates a syntax error in the SPF | |
348 | record of the queried domain. This should be | |
349 | treated like "none". | |
350 | o err_temp This indicates a temporary error during all | |
3ec3e3bb | 351 | processing, including Exim's SPF processing. |
ee161e8f | 352 | You may defer messages when this occurs. |
8ff3788c | 353 | |
ee161e8f PH |
354 | You can prefix each string with an exclamation mark to invert |
355 | is meaning, for example "!fail" will match all results but | |
356 | "fail". The string list is evaluated left-to-right, in a | |
357 | short-circuit fashion. When a string matches the outcome of | |
358 | the SPF check, the condition succeeds. If none of the listed | |
359 | strings matches the outcome of the SPF check, the condition | |
360 | fails. | |
361 | ||
f413481d TK |
362 | Here is an example to fail forgery attempts from domains that |
363 | publish SPF records: | |
ee161e8f PH |
364 | |
365 | /* ----------------- | |
f413481d TK |
366 | deny message = $sender_host_address is not allowed to send mail from ${if def:sender_address_domain {$sender_address_domain}{$sender_helo_name}}. \ |
367 | Please see http://www.openspf.org/Why?scope=${if def:sender_address_domain {mfrom}{helo}};identity=${if def:sender_address_domain {$sender_address}{$sender_helo_name}};ip=$sender_host_address | |
ee161e8f PH |
368 | spf = fail |
369 | --------------------- */ | |
370 | ||
371 | You can also give special treatment to specific domains: | |
372 | ||
373 | /* ----------------- | |
374 | deny message = AOL sender, but not from AOL-approved relay. | |
375 | sender_domains = aol.com | |
376 | spf = fail:neutral | |
377 | --------------------- */ | |
378 | ||
379 | Explanation: AOL publishes SPF records, but is liberal and | |
380 | still allows non-approved relays to send mail from aol.com. | |
381 | This will result in a "neutral" state, while mail from genuine | |
382 | AOL servers will result in "pass". The example above takes | |
383 | this into account and treats "neutral" like "fail", but only | |
384 | for aol.com. Please note that this violates the SPF draft. | |
385 | ||
386 | When the spf condition has run, it sets up several expansion | |
387 | variables. | |
388 | ||
389 | $spf_header_comment | |
390 | This contains a human-readable string describing the outcome | |
391 | of the SPF check. You can add it to a custom header or use | |
392 | it for logging purposes. | |
8ff3788c | 393 | |
ee161e8f | 394 | $spf_received |
8fe685ad | 395 | This contains a complete Received-SPF: header that can be |
ee161e8f PH |
396 | added to the message. Please note that according to the SPF |
397 | draft, this header must be added at the top of the header | |
398 | list. Please see section 10 on how you can do this. | |
8ff3788c | 399 | |
65a7d8c3 NM |
400 | Note: in case of "Best-guess" (see below), the convention is |
401 | to put this string in a header called X-SPF-Guess: instead. | |
402 | ||
ee161e8f PH |
403 | $spf_result |
404 | This contains the outcome of the SPF check in string form, | |
405 | one of pass, fail, softfail, none, neutral, err_perm or | |
406 | err_temp. | |
8ff3788c | 407 | |
ee161e8f PH |
408 | $spf_smtp_comment |
409 | This contains a string that can be used in a SMTP response | |
410 | to the calling party. Useful for "fail". | |
8ff3788c | 411 | |
65a7d8c3 NM |
412 | In addition to SPF, you can also perform checks for so-called |
413 | "Best-guess". Strictly speaking, "Best-guess" is not standard | |
414 | SPF, but it is supported by the same framework that enables SPF | |
415 | capability. Refer to http://www.openspf.org/FAQ/Best_guess_record | |
416 | for a description of what it means. | |
417 | ||
418 | To access this feature, simply use the spf_guess condition in place | |
419 | of the spf one. For example: | |
420 | ||
421 | /* ----------------- | |
422 | deny message = $sender_host_address doesn't look trustworthy to me | |
423 | spf_guess = fail | |
424 | --------------------- */ | |
425 | ||
426 | In case you decide to reject messages based on this check, you | |
427 | should note that although it uses the same framework, "Best-guess" | |
428 | is NOT SPF, and therefore you should not mention SPF at all in your | |
429 | reject message. | |
430 | ||
431 | When the spf_guess condition has run, it sets up the same expansion | |
432 | variables as when spf condition is run, described above. | |
433 | ||
434 | Additionally, since Best-guess is not standarized, you may redefine | |
435 | what "Best-guess" means to you by redefining spf_guess variable in | |
436 | global config. For example, the following: | |
437 | ||
438 | /* ----------------- | |
439 | spf_guess = v=spf1 a/16 mx/16 ptr ?all | |
440 | --------------------- */ | |
441 | ||
442 | would relax host matching rules to a broader network range. | |
8ff3788c | 443 | |
ee161e8f | 444 | |
0b23848a | 445 | SRS (Sender Rewriting Scheme) Support |
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446 | -------------------------------------------------------------- |
447 | ||
448 | Exiscan currently includes SRS support via Miles Wilton's | |
8ff3788c | 449 | libsrs_alt library. The current version of the supported |
ee161e8f PH |
450 | library is 0.5. |
451 | ||
452 | In order to use SRS, you must get a copy of libsrs_alt from | |
453 | ||
454 | http://srs.mirtol.com/ | |
455 | ||
456 | Unpack the tarball, then refer to MTAs/README.EXIM | |
457 | to proceed. You need to set | |
458 | ||
459 | EXPERIMENTAL_SRS=yes | |
460 | ||
461 | in your Local/Makefile. | |
462 | ||
463 | ||
464 | -------------------------------------------------------------- | |
465 | End of file | |
466 | -------------------------------------------------------------- |