X-Git-Url: https://git.exim.org/users/jgh/exim.git/blobdiff_plain/4df1e33e03e9edf6ee6cd328114e5eb102a85c9c..ca02eafb3654a6539abb59a0f3ce4c52fe97f20e:/doc/doc-txt/NewStuff diff --git a/doc/doc-txt/NewStuff b/doc/doc-txt/NewStuff index ba1c5afc4..65b0fc678 100644 --- a/doc/doc-txt/NewStuff +++ b/doc/doc-txt/NewStuff @@ -1,4 +1,4 @@ -$Cambridge: exim/doc/doc-txt/NewStuff,v 1.44 2005/05/23 15:44:06 fanf2 Exp $ +$Cambridge: exim/doc/doc-txt/NewStuff,v 1.50 2005/06/16 20:03:43 tom Exp $ New Features in Exim -------------------- @@ -121,6 +121,228 @@ TF/03 The control = fakereject ACL modifier now has a fakedefer counterpart, to be duplicated when the sender retries. Therefore you should not use fakedefer if the message will be delivered normally. +TF/04 There is a new ratelimit ACL condition which can be used to measure + and control the rate at which clients can send email. This is more + powerful than the existing smtp_ratelimit_* options, because those + options only control the rate of commands in a single SMTP session, + whereas the new ratelimit condition works across all connections + (concurrent and sequential) to the same host. + + The syntax of the ratelimit condition is: + + ratelimit = /

/ / + + If the average client sending rate is less than m messages per time + period p then the condition is false, otherwise it is true. + + The parameter p is the smoothing time constant, in the form of an Exim + time interval e.g. 8h for eight hours. A larger time constant means it + takes Exim longer to forget a client's past behaviour. The parameter m is + the maximum number of messages that a client can send in a fast burst. By + increasing both m and p but keeping m/p constant, you can allow a client + to send more messages in a burst without changing its overall sending + rate limit. Conversely, if m and p are both small then messages must be + sent at an even rate. + + The key is used to look up the data used to calcluate the client's + average sending rate. This data is stored in a database maintained by + Exim in its spool directory alongside the retry database etc. For + example, you can limit the sending rate of each authenticated user, + independent of the computer they are sending from, by setting the key + to $authenticated_id. The default key is $sender_host_address. + + Each ratelimit condition can have up to two options. The first option + specifies what Exim measures the rate of, and the second specifies how + Exim handles excessively fast clients. + + The per_mail option means that it measures the client's rate of sending + messages. This is the default if none of the per_* options is specified. + + The per_conn option means that it measures the client's connection rate. + + The per_byte option limits the sender's email bandwidth. Note that it + is best to use this option in the DATA ACL; if it is used in an earlier + ACL it relies on the SIZE parameter on the MAIL command, which may be + inaccurate or completely missing. You can follow the limit m in the + configuration with K, M, or G to specify limits in kilobytes, + megabytes, or gigabytes respectively. + + The per_cmd option means that Exim recomputes the rate every time the + condition is processed, which can be used to limit the SMTP command rate. + The alias per_rcpt is provided for use in the RCPT ACL instead of per_cmd + to make it clear that the effect is to limit the rate at which recipients + are accepted. Note that in this case the rate limiting engine will see a + message with many recipients as a large high-speed burst. + + If a client's average rate is greater than the maximum, the rate + limiting engine can react in two possible ways, depending on the + presence of the strict or leaky options. This is independent of the + other counter-measures (e.g. rejecting the message) that may be + specified by the rest of the ACL. The default mode is leaky, which + avoids a sender's over-aggressive retry rate preventing it from getting + any email through. + + The strict option means that the client's recorded rate is always + updated. The effect of this is that Exim measures the client's average + rate of attempts to send email, which can be much higher than the + maximum. If the client is over the limit it will be subjected to + counter-measures until it slows down below the maximum rate. + + The leaky option means that the client's recorded rate is not updated + if it is above the limit. The effect of this is that Exim measures the + client's average rate of successfully sent email, which cannot be + greater than the maximum. If the client is over the limit it will + suffer some counter-measures, but it will still be able to send email + at the configured maximum rate, whatever the rate of its attempts. + + As a side-effect, the ratelimit condition will set the expansion + variables $sender_rate containing the client's computed rate, + $sender_rate_limit containing the configured value of m, and + $sender_rate_period containing the configured value of p. + + Exim's other ACL facilities are used to define what counter-measures + are taken when the rate limit is exceeded. This might be anything from + logging a warning (e.g. while measuring existing sending rates in order + to define our policy), through time delays to slow down fast senders, + up to rejecting the message. For example, + + # Log all senders' rates + warn + ratelimit = 0 / 1h / strict + log_message = \ + Sender rate $sender_rate > $sender_rate_limit / $sender_rate_period + + # Slow down fast senders + warn + ratelimit = 100 / 1h / per_rcpt / strict + delay = ${eval: 10 * ($sender_rate - $sender_rate_limit) } + + # Keep authenticated users under control + deny + ratelimit = 100 / 1d / strict / $authenticated_id + + # System-wide rate limit + defer + message = Sorry, too busy. Try again later. + ratelimit = 10 / 1s / $primary_hostname + + # Restrict incoming rate from each host, with a default rate limit + # set using a macro and special cases looked up in a table. + defer + message = Sender rate $sender_rate exceeds \ + $sender_rate_limit messages per $sender_rate_period + ratelimit = ${lookup {$sender_host_address} \ + cdb {DB/ratelimits.cdb} \ + {$value} {RATELIMIT} } + +TK/01 Added an 'spf' lookup type that will return an SPF result for a given + email address (the key) and an IP address (the database): + + ${lookup {tom@duncanthrax.net} spf{217.115.139.137}} + + The lookup will return the same result strings as they can appear in + $spf_result (pass,fail,softfail,neutral,none,err_perm,err_temp). The + lookup is armored in EXPERIMENTAL_SPF. Currently, only IPv4 addresses + are supported. + + Patch submitted by Chris Webb . + +PH/02 There's a new verify callout option, "fullpostmaster", which first acts + as "postmaster" and checks the recipient . If that + fails, it tries just , without a domain, in accordance with + the specification in RFC 2821. + +PH/03 The action of the auto_thaw option has been changed. It no longer applies + to frozen bounce messages. + +TK/02 There are two new expansion items to help with the implementation of + the BATV "prvs" scheme in an Exim configuration: + + + ${prvs {

}{}{[KEYNUM]}} + + The "prvs" expansion item takes three arguments: A qualified RFC2821 + email address, a key and an (optional) key number. All arguments are + expanded before being used, so it is easily possible to lookup a key + and key number using the address as the lookup key. The key number is + optional and defaults to "0". The item will expand to a "prvs"-signed + email address, to be typically used with the "return_path" option on + a smtp transport. The decision if BATV should be used with a given + sender/recipient pair should be done on router level, to avoid having + to set "max_rcpt = 1" on the transport. + + + ${prvscheck {
}{}{}} + + The "prvscheck" expansion item takes three arguments. Argument 1 is + expanded first. When the expansion does not yield a SYNTACTICALLY + valid "prvs"-scheme address, the whole "prvscheck" item expands to + the empty string. If
is a "prvs"-encoded address after + expansion, two expansion variables are set up: + + $prvscheck_address Contains the "prvs"-decoded version of + the address from argument 1. + + $prvscheck_keynum Contains the key number extracted from + the "prvs"-address in argument 1. + + These two variables can be used in the expansion code of argument 2 + to retrieve the . The VALIDITY of the "prvs"-signed address + is then checked. The result is stored in yet another expansion + variable: + + $prvscheck_result Contains the result of a "prvscheck" + expansion: Unset (the empty string) for + failure, "1" for success. + + The "prvscheck" expansion expands to the empty string if
+ is not a SYNTACTICALLY valid "prvs"-scheme address. Otherwise, + argument 3 defines what "prvscheck" expands to: If argument 3 + is the empty string, "prvscheck" expands to the decoded version + of the address (no matter if it is CRYPTOGRAPHICALLY valid or not). + If argument 3 expands to a non-empty string, "prvscheck" expands + to that string. + + + Usage example + ------------- + + Macro: + + PRVSCHECK_SQL = ${lookup mysql{SELECT secret FROM batv_prvs WHERE \ + sender='${quote_mysql:$prvscheck_address}'}{$value}} + + RCPT ACL: + + # Bounces: drop unsigned addresses for BATV senders + deny message = This address does not send an unsigned reverse path. + senders = : + recipients = +batv_recipients + + # Bounces: In case of prvs-signed address, check signature. + deny message = Invalid reverse path signature. + senders = : + condition = ${prvscheck {$local_part@$domain}{PRVSCHECK_SQL}{1}} + !condition = $prvscheck_result + + Top-Level Router: + + batv_redirect: + driver = redirect + data = ${prvscheck {$local_part@$domain}{PRVSCHECK_SQL}{}} + + Transport (referenced by router that makes decision if + BATV is applicable): + + external_smtp_batv: + driver = smtp + return_path = ${prvs {$return_path} \ + {${lookup mysql{SELECT \ + secret FROM batv_prvs WHERE \ + sender='${quote_mysql:$sender_address}'} \ + {$value}fail}}} + + Version 4.51 ------------