What are Transport Dumpster and SafetyNet in Exchange Server?

In this article, we are going to look what is meant by transport dumpster and safetynet in Exchange server and its feature.


Transport Dumpster and Shadow Redundancy together forms the Transport High Availability. Transport Dumpster is a feature to protect emails that are in transit. We have multiple options to protect and backup messages that have reached the database, but when the email is in transit if a server goes down the email will be lost. Hence to protect those emails Microsoft came up with this idea of Transport Dumpster. By this feature emails will not be lost in transit or even after losing there will be a backup (Transport Database) that can be re-sent and Exchange Systems or the end-user will not face any data loss.

This feature was first introduced in Exchange 2007 server for replicated databases only. Hence the feature of transport dumpster applies only for Continuous Cluster Replication (CCR) & Local Cluster Replication (LCR) in Exchange 2007, as Microsoft introduced the concept called Database Availability Groups (DAG) in Exchange 2010, this feature got enhanced. Still non-replicated database, mails sent to Public Folders etc., were not protected. This border-line were the Transport Dumpster safeguards the email is technically called as Transport boundary. As already mentioned Transport boundary limits only with-in the replicated Database (2007), Database in a DAG (2010). Microsoft enhanced this feature in Exchange 2013 and they renamed it as SafetyNet.


SafetyNet is the advanced version of Transport dumpster and it was introduced in Exchange 2013. SafetyNet was mainly introduced to safe guard the emails that are sent to non-replicated database, Public Folders. Until Exchange 2010 all the emails must go through Hub Transport Server, But In Exchange 2013 there is no dedicated Hub Role, it was split and given to Client Access Server and Mailbox Database Server. This option offered Microsoft to extend the Transport Boundary. So SafetyNet is capable of securing emails for which lacked in its predecessors. This redefined the Transport Boundary and the complications of previous versions are simplified. Boundary of SafetyNet is,

  1. Single Database Availability Group – All the Mailbox Database, Public Folder Mailboxes inside a DAG.
  2. Logical Active Directory Site – All the Mailbox Database, Public Folders, in a Single AD Site, even though they are not a part DAG it is bounded inside SafetyNet.

SafetyNet by itself is made Redundant, unlike its Predecessors SafetyNet holds its redundant copy in a different boundary and it is called as ShadowNet.

Transport Database:

All the above discussed data is been saved in a single file call “mail.que”. This file is the Transport Database, which saves all the emails in transit, and provides redundancy. Until Exchange 2010 mail will be kept in this database for a defined time limit after which that email will be purged irrespective of the delivery of that email. But in SafetyNet it holds the email until it receives the successful acknowledgment from the Next Transport Boundary or the Mailbox. SafetyNet creates a redundant secondary mail queue and safely holds the email in that queue also. This queue will be held active until it receives the acknowledgment. Once the acknowledgement is received this mail will be dropped from that queue. This concept is called as Shadow Redundancy. We can view the complete queue in Exchange Powershell using the command “Get-TransportServer | Get-Queue”. This will display all the mail queues in all the Hub Servers and services.

Transport High Availability Configurations:

Transport Dumpster settings can be viewed through Exchange Powershell. Below are the Settings that define the Transport High Availability.Settings That Define The Transport High Availability

SafetyNet Settings:SafetyNet Settings


Transport Dumpster and SafetyNet are the some of the important concepts since they deal with the High Availability of Exchange Systems. If you wish to learn more about Microsoft Exchange it is advisable to learn other High Availability such as DAG etc., we can expect some more advancement in forthcoming versions of Exchange Systems. As I always mentioned before we need to be ready to face any recovery option if there are any failures. It is good to consider OST to PST conversion option if we need to recover the data.

Author Introduction:

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

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