Planning Transport Rules
Transport rules provide you with an almost limitless ability to control messaging in your Exchange Server organization. Always carefully plan your transport rules to ensure that they behave as intended. Otherwise, you could accidentally delete messages, or deliver messages to unintended recipients.
Consider the following recommendations when you plan transport rules:
- Plan conditions and exceptions carefully. Transport rule conditions and exceptions define which messages are affected by the transport rule. If you implement the rules incorrectly, you may unintentionally modify or delete messages.
- Plan for Transport rule priority and order. In many cases, you will have to apply several transport rules in your organization. If these transport rules have conditions that can overlap in some cases, it is very important that you order them properly.
- Use regular expressions to check message contents. Use regular expressions to simplify the list of terms when you are including a text string in a condition. You can use one regular expression, rather than a list of variations on the same word. For example, when searching for a phone-number pattern, you can use the expression “\d\d\d(-|.)\d\d\d\d”, which denotes a pattern of three digits, then a dot or dash, and then four digits.
- Test application of transport rules. Test new transport rules to ensure they behave as intended. This is important because a new transport rule could conflict with existing transport rules.
- Plan for transport rule limitations on encrypted and digitally signed messages. AD RMS integration with Exchange Server 2016 enables you to implement transport rules and messaging policies when you are using AD RMS Information Rights Management encryption to protect messages. Encryption through other mechanisms may prevent you from applying transport rules or records management. For example, Exchange Server may not be able to scan encrypted messages for the text string specified in a transport rule. In addition, antivirus scanners cannot scan messages with encrypted attachments.
- Consider transport rule recovery. Deleted transport rules are not easily recoverable. Transport rules are stored in AD DS, and restoring rules from AD DS is a complex process. Alternatively, documented transport rules are easy to re-create, and you can export transport rules to backup files by using the Export-TransportRuleCollection cmdlet. However, when you import transport rules onto a Hub Transport server, the server replaces all of the existing transport rules for the organization.