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The Exchange tarpitting interval must be set.


Finding ID Version Rule ID IA Controls Severity
V-69891 EX13-EG-000240 SV-84513r1_rule Medium
Tarpitting is the practice of artificially delaying server responses for specific Simple Mail Transfer Protocol (SMTP) communication patterns that indicate high volumes of spam or other unwelcome messages. The intent of tarpitting is to slow down the communication process for spam batches to reduce the cost effectiveness of sending spam and thwart directory harvest attacks. A directory harvest attack is an attempt to collect valid email addresses from a particular organization so the email addresses can be added to a spam database. A program can be written to collect email addresses that return a "Recipient OK" SMTP response and discard all email addresses that return a "User unknown" SMTP response. Tarpitting makes directory harvest attacks too costly to automate efficiently.
MS Exchange 2013 Edge Transport Server Security Technical Implementation Guide 2019-03-11


Check Text ( C-70359r1_chk )
Open the Exchange Management Shell and enter the following command:

Get-ReceiveConnector | Select Name, Identity, TarpitInterval

For each Receive connector, if the value of TarpitInterval is not set to 00:00:05 or greater, this is a finding.
Fix Text (F-76121r1_fix)
Open the Exchange Management Shell and enter the following command:

Set-ReceiveConnector -Identity <'IdentityName'> -TarpitInterval '00:00:05'

Note: The value and 00:00:05 must be in quotes.

Repeat the procedures for each Receive connector.