X-Git-Url: https://git.exim.org/exim.git/blobdiff_plain/03fc05ca1d6e5d7a5baf40000c3963a5ed1b0fa7..b003ce30f0038c2042303d18fc24f278de06a1f5:/doc/doc-docbook/spec.xfpt

diff --git a/doc/doc-docbook/spec.xfpt b/doc/doc-docbook/spec.xfpt
index cea21a18f..0385de6db 100644
--- a/doc/doc-docbook/spec.xfpt
+++ b/doc/doc-docbook/spec.xfpt
@@ -32315,6 +32315,14 @@ content-scanning extension, and is available only in the DATA, MIME, and
 non-SMTP ACLs. It causes the incoming message to be scanned for a match with
 any of the regular expressions. For details, see chapter &<<CHAPexiscan>>&.
 
+.new
+.vitem &*seen&~=&~*&<&'parameters'&>
+.cindex "&%sseen%& ACL condition"
+This condition can be used to test if a situation has been previously met,
+for example for greylisting.
+Details are given in section &<<SECTseen>>&.
+.wen
+
 .vitem &*sender_domains&~=&~*&<&'domain&~list'&>
 .cindex "&%sender_domains%& ACL condition"
 .cindex "sender" "ACL checking"
@@ -33039,6 +33047,59 @@ address you should specify alternate list separators for both the outer
        dnslists = <; dnsbl.example.com/<|$acl_m_addrslist
 .endd
 
+
+.new
+.section "Previously seen user and hosts" "SECTseen"
+.cindex "&%sseen%& ACL condition"
+.cindex greylisting
+The &%seen%& ACL condition can be used to test whether a
+situation has been previously met.
+It uses a hints database to record a timestamp against a key.
+host. The syntax of the condition is:
+.display
+&`seen =`& <&'time interval'&> &`/`& <&'options'&>
+.endd
+
+For example,
+.code
+defer	seen = -5m / key=${sender_host_address}_$local_part@$domain
+.endd
+in a RCPT ACL will implement simple greylisting.
+
+The parameters for the condition
+are an interval followed, slash-separated, by a list of options.
+The interval is taken as an offset before the current time,
+and used for the test.
+If the interval is preceded by a minus sign then the condition returns
+whether a record is found which is before the test time.
+Otherwise, the condition returns whether one is found which is since the
+test time.
+
+Options are read in order with later ones overriding earlier ones.
+
+The default key is &$sender_host_address$&.
+An explicit key can be set using a &%key=value%& option.
+
+If a &%readonly%& option is given then
+no record create or update is done.
+If a &%write%& option is given then
+a record create or update is always done.
+An update is done if the test is for &"since"&.
+
+Creates and updates are marked with the current time.
+
+Finally, a &"before"& test which succeeds, and for which the record
+is old enough, will be refreshed with a timestamp of the test time.
+This can prevent tidying of the database from removing the entry.
+The interval for this is, by default, 10 days.
+An explicit interval can be set using a
+&%refresh=value%& option.
+
+Note that &"seen"& should be added to the list of hints databases
+for maintenance if this ACL condition is used.
+.wen
+
+
 .section "Rate limiting incoming messages" "SECTratelimiting"
 .cindex "rate limiting" "client sending"
 .cindex "limiting client sending rates"