How to Configure an Exchange 2010 SMTP Connector

How to Configure an Exchange 2010 SMTP ConnectorConfigure Exchange 2010 SMTP Connector

The golden rule with Exchange 2010 SMTP connectors is don’t do more than you have to.  You probably need internet access, therefore by all means configure an SMTP connector to your ISP.  However, if you have multiple Exchange 2010 servers in the same site then they can communicate effectively without SMTP connectors.

One surprise is that Exchange 2010 SMTP connectors are uni-directional, thus to link two servers, you need one connector to receive and another to send email.

Topics for Configuring Exchange 2010 SMTP Connectors


Exchange 2010 Routing Strategies

Routing Strategies For Local Email

Emails addressed to recipients in the local Active Directory site are handled by the Hub Transport server.  It’s the job of the categorizer to deliver the email to the correct mailbox server; whereupon the message is retrieved by a version of Outlook.

Routing Strategies For Remote Email

  1. Internal to Hub Transport –> Hub Transport different Active Directory site.
  2. Internal to Hub Transport server –> ISP Internet
  3. Internal to Hub Transport server –> Edge –> Internet

Receiving email uses the same routes as above, but in reverse.  Thus it follows that you can categorize messages into four groups: inbound or outbound, and local or remote.

Because every delivery strategy involves the Hub Transport server, you can appreciate why every Exchange 2010 organization needs at least one server with this role.  Indeed, Microsoft’s recommendation is to have one server with the Hub Transport role in each Active Directory site.

Supporting Components for the Exchange 2010 SMTP Connectors

While the categorizer is at the heart of the message system, let us get to know the other important components, the Microsoft Exchange Mail Submission service, store driver and the submission queue.

  1. As soon as an Outlook users sends an email, the Microsoft Exchange Mail Submission service takes over.
  2. The Submission service then notifies a Hub Transport server in the local Active Directory site.
  3. The email is then sent to the for the categorizer’s submission queue.
  4. The store driver uses MAPI to connects to a user’s ‘Outbox’ folder, it then retrieves the message from the corresponding Mailbox server. 
  5. Then the store driver converts the MAPI format into the Summary-Transport Neutral Encapsulation Format (S/TNEF).  This format has no plain text part, and is in eight-bit binary format.
  6. Next, the store driver places the email into the submission queue and moves the message from the user’s ‘Outbox’ to their ‘Sent Items’ folder.

Message Delivery

In addition to local delivery, email can also enter the submission queue from an SMTP Receive connector, or even from the Pickup directory.  The submission queue stores all messages safely on disk until the categorizer is ready to process them.

It is the categorizer that is responsible for calculating the best routing path, for converting content format, and applying any organizational message policies.  Incidentally, the categorizer on an Edge Transport server verifies the recipient’s SMTP address of an inbound message before it places it in the delivery queue.

The incoming message is then routed to a Hub Transport server.  In a new development in Exchange 2010, the categorizer makes copies of messages that have multiple recipients.

The categorizer processes each message in the submission queue in turn. If a message is intended for a Mailbox server in the same Active Directory site, the categorizer places the message in a local delivery queue.  The store driver then takes over and delivers the message to the Mailbox server role by using MAPI.

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How to Configure an Exchange 2010 SMTP ConnectorExchange 2010 Hub Connectors

The logical place to create an SMTP connector is on the server(s) with the Hub Transport role.  The other place to configure these Exchange 2010 send and receive connectors would be on the Edge Server.

  • Launch the Exchange Management Console.
  • Check the Organizational Configuration node.
  • Observe the Hub Transport node.
  • Check the Server Configuration.
  • Click on this second Hub Transport node.
  • This is where you create or edit the Send and Receive Connectors.

Receive Connectors

Receive connectors represent a gateway through which all inbound messages are enter your Exchange 2010 Server.  You need a receive connectors for each server, and they control how that server takes delivery of messages from the Internet or email clients.

Luckily, the receive connectors required for internal mail flow are automatically created when you install the Hub or Edge Transport server role.

Once you create a Receive Connector you can tweak its Properties.  Suppose you have a partner company, you can specify the source IP addresses from where you receive messages.  Also, in the Limits tab you can adjust the maximum size of messages and configure permissions.  And for troubleshooting messages, you could enable protocol logging on the General tab of Exchange 2010 SMTP connector.

Exchange 2010 SMTP Connector Limits

PowerShell RecieveConnector Cmdlets (Exchange Management Shell)

As an alternative to configuring through the Exchange Management Console, is to use PowerShell to manage the Exchange 2010 SMTP connectors. 

Get-ReceiveConnector -Server YourExch

Note 1: You need to change the value for ‘-Server YourExch’

Note 2: This is how you could research more of these cmdlets:

Get-command *ReceiveConnector

This reveals the ReceiveConnector family of Powershell Cmdlets

  • Get-ReceiveConnector
  • Set-ReceiveConnector
  • New-ReceiveConnector
  • Remove-ReceiveConnector

New-ReceiveConnector -Name ‘Receive from ISP’ `
-Type FromInternet `
-Bindings -RemoteIPRanges


New-ReceiveConnector -Name ‘Receive from Central’ `
-Type FromEnterprise -Bindings `
-RemoteIPRanges `
-RelayControl Open

How to Configure Internet Email in Exchange 2010 Server

In Exchange 2003, all internet mail is directed through the SMTP virtual server.  However in Exchange 2010 server, the SMTP virtual server no longer handles internet email, instead this task is performed by the new SMTP connector.Internet Email in Exchange 2010 Server

Internet emails are typically routed by the Hub Transport via an Edge server subscription.  Alternatively, you could create a Send connector on the Hub Transport server itself, and configure it to deliver outgoing internet email.

  • Launch the Exchange Management Console.
  • Expand the Organizational Configuration node.
  • Select the Hub Transport node.
  • Click on the Send Connectors.
  • In the Actions pane, select New Send Connector.
  • The Wizard will guide you through the options.  In particular look for the Internet option from the drop down box.
  • Choose a Smart Host, or DNS MX records to send the email.

PowerShell SendConnector

Alternatively you can use the New-SendConnector cmdlet in the Exchange Management Shell.  Note, as you create the new Send Connector, observe the PowerShell code on the last screen, just before the wizard completes.

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Exchange 2003 Features not supported in Exchange 2010

Enabled/disabled property
Exchange Server 2003 cannot detect the status of an Exchange Server 2010 connector, therefore it will continue routing, even if a connector is disabled.

Maximum message size
If you have two connectors, one from Exchange 2003 and another from 2010, then make sure that the message size limits are the same.  If not, then the lower value will be the restriction that is in force.

Other Restrictions not enforced
In addition, these settings are not supported in Exchange 2010: Message priority, Message type, and Per user delivery restriction.

Firewall Rules – Suggestions


  1. Allow port 25 to and from all external IP addresses to the Edge Transport server.  (Since this is the default port required for SMTP email delivery.)
  2. Open port 53 to all external IP addresses from the Edge Transport server.   You need this port for the Edge server to resolve DNS names on the Internet.


  1. Again, port 25 is the default port for SMTP. Allow this port to and from the Edge Transport server to specified Hub Transport servers.
  2. Allow port 50636 for LDAPS (Secure Lightweight Directory Access Protocol) from specified Hub Transport servers to the Edge Transport server.  This port is used specifically for the Edge Synchronization process.

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Exchange 2010 Send Connectors – Designing Outbound Message Flow

Send connectors create a logical connection to remote email systems and are responsible for outbound transmissions.  When you use the EdgeSync process, it will configure the Send connectors automatically.  Alternatively, you can create the Send Connectors manually with either the EMC or the Shell.

When designing outbound message flow in Exchange 2010, consider the following factors:

Will you use a single location for routing all messages to the Internet?  Or will you enable message routing through multiple locations?  If your organization has more than one location with an Internet connection, you can enable message routing through each. To do this, you can either:

  • Install an Edge Transport server in each location and configure edge subscriptions between the Edge Transport servers and the local Active Directory sites.
  • Manually configure Send connectors on the Hub Transport or Edge Transport servers.

On the one hand, the advantage of a single route is security. You need be concerned only with a single connection, from the internal network to the Internet.  On the other hand, multiple routes provide redundancy and load balancing.

Internal Send Connectors
You probably won’t need to create internal Send connectors, because they are created automatically when you add the Hub Transport role. 

Partner This type of connector is used to forward messages to partner domains. Partner connectors allow connections only to SMTP servers that authenticate using TLS certificates.

Custom Send Connector
The time to establish extra Send connectors is when you want to create direct routes rather than using the internet. With this type of Send connector, you specify the address space and the smart host.  Keep in mind that if you create another Send connector, that connector can be used by any Hub Transport server in your organization. This is because all configuration data is stored in Active Directory.

Receive Connectors – Designing Inbound Message Flow

In addition to the security v redundancy factors, which apply email in both directions, inbound message flow has extra challenges.  Firstly remember that receive connectors just affect the local server, whereas send connectors affect the entire Exchange organization.

The key point with a receive connector is that it must contain a unique combination of: IP address bindings, port-number assignments, and the remote IP address ranges.  One reason of creating extra receive connectors is that particular sources require authentication.

How are you are going to plan for MX record with multiple inbound routing points?   If you configure MX records with different priorities, then the SMTP servers with the lowest priority MX record references are contacted first for all inbound messages.  MX records with higher priorities are only referenced when the first SMTP server is not available.

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Using Telnet to Test Exchange 2010 SMTP Connections

In Windows Server 2008, the Telnet Client is disabled by default.  Therefore you need to enable it by:

  • Open Server Manager.
  • Click Action, and then select Add Features.
  • Select Telnet Client, and then click Next.
  •  Click Install, and then click Close

Using Telnet in Exchange Server 2010

Telnet is a marvellous command for basic SMTP troubleshooting.  There are two tricks to using telnet in this situation:
1) type: Set LocalEcho
2) Remember to specify port 25, because Telnet normally uses TCP port 23.

Launch a cmd or PowerShell session

set localecho
Open server port for example:
Open exchserver 25
Open 25

Hopefully you get a reply such as:
220 Microsoft ESMTP MAIL Service ready at Wed, 30 March 2011

Type: Quit. This will exit Telnet.

More Info Testing SMTP with Telnet


Preliminary preparation to use telnet to test an SMTP connection

Destination SMTP server

Source domain

Sender’s e-mail address [email protected]

Recipient’s e-mail address [email protected]

Message subject Test from Guy

Message body This is Guy’s message

At the command prompt:

Type:  MAIL FROM:[email protected]  and then press ENTER.

Type:  RCPT TO:[email protected]  NOTIFY=success,failure

Type:  DATA

Type:  Subject: Test from Guy and then press ENTER

Press:  Enter Again

Type: This is Guy’s message and then press ENTER

Press: Enter

Type . (dot or period) press ENTER again

Expect: 250 2.6.0 <GUID> Queued mail for delivery

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See more Microsoft Exchange Server 2010 topics:

Exchange Home  • Exchange 2010 Transition  • Exchange 2010 Migration  • Exchange 2010 SP1

• Exchange MX Records  • Exchange 2010 Logs  • Exchange 2010 Circular Logging  • Exchange Stores

Exchange 2010 GAL  • Exchange 2010 SMTP Connector  • Free Exchange Monitor  • Home