In-Depth Understanding of Transport Rules in Exchange Server

In this article, we are going to see how the transport rules works in Exchange servers and its functionalities in detail.


Transport Rules are defined in the Exchange Systems to efficiently control, moderate and divert the mail flow as per our requirements. These rules take complete control of all the Incoming and outgoing emails and action as per the scope of the rule.Transport Rules

These rules are acting upon mails before it reaches the mailbox at server end. Once the mails are reached mailbox, then if the outlook is configured in cached mode, we can recover it through OST 2 PST method, if there are any data loss at server end.

Major Usage of Transport Rules:

Some of the major users as follows,

  1. Used to append disclaimers at the end of each outgoing email
  2. Moderate emails based on sender, recipient, attachment and contents. These emails can also be diverted for approval to stake holders
  3. Add recipients, Redirect, Block, Delete, Add additional info to message headers/Subject line etc. Notify the sender with policy tip
  4. Message securities can be modified, emails can be encrypted using IRM and much more

How Transport Rules works:

Condition Action And ExceptionThey work on the below Concept.

  1. Condition
  2. Exception (optional)
  3. Action

Every Transport rule should have a condition and an action. Exception is an optional parameter that can used to exclude some emails or users from this rule.

Condition: Condition is the parameter that defines the work scope of this transport rule. Examples of Condition are “If the Sender is”, “If the message properties has the value” etc. These granular conditions are called as predicates.

Exception: Exception allows the administrators to exclude certain users or emails, so that this transport rule will not applied on them. Examples for Exceptions are “If member of a Distribution group”, “If the Recipient is” etc.

Action: Action is the task that should be performed on that email. If can be delete the email, divert the email for approval. Append warnings in subject line for spam emails etc.

A single transport rule can have multiple values for all the 3 parameters. Every transport rule will a have priority assigned, we can increase or decrease it anytime. Also these rules should be enabled after creating it, else this rule will not act upon emails even the condition is met.

Order on how the rules are applied:

There is a pre-defined order to process the rule on each and every emails.

  1. Message scope:Transport rule agents check if this email falls under this category.
  2. Priority: All the Transport rule will have a priority assigned and it start with ‘0’ as the first priority and keeps increasing
  3. Conditions   The Granular predicates that determines the conditions.
  4. Rule with no conditions:A rule with no condition and no exceptions is applied to all messages.
  5. Rule with multiple predicates:A rule with a multiple Conditions
  6. Exceptions: If any matches the exception list defined in that rule that the Transport rule is not applied
  7. Actions: Finally, based on the action implemented on the Transport rule.

Other Options: Other options available in the Transport rule are

  1. Stop Processing More rules – If this option is enabled, the transport agent will not check for other transport rules.
  2. Activation and Deactivation Dates – We can set activation and deactivation dates for a rule so that it can automatically enable or disable as mentioned in the rule.
  3. Rule Mode – It is used to determine whether the rule is in production (enabled) or in testing (using policy tips)


Apart from the above mentioned options there are lot more available, we need to use our logical thinking for creating transport rules for complex requirements. So I would recommend you to explore these rules and expertise yourself in this concept 🙂

Author Introduction:

Sophia Mao is a data recovery expert in DataNumen, Inc., which is the world leader in data recovery technologies, including repair pst file corruption and word recovery software products. For more information visit

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