I have a client that has a need for automatic failover of send connectors. The client currently has a send connector that resolves to a smart host and sends to the internet. I need to setup a way that if the smarthost goes down the mail will automatically route directly to the internet. I have attempted to setup another send connector with a higher cost and I have it set to route via MX, But when I simulate failure of the smarthost and send messages they get stuck in the smarthost queue.

I am looking for options to resolve this request. Thanks in advance for your help!

Hi ,

What happens if you do like below ? Does exchange will automatically fail over to the next smart host mentioned on the send connector ?

Just have a single send connector with both the smart host ip address and then down anyone of the smarthost for a checking purpose.

 This only works if I want to use another smart host. I want to alternatively use MX to process the send. Thank you for your reply.

I have found this article which helps further understand the processing of external email of 2010. I haven't found the equivalent article for 2013.

https://technet.microsoft.com/en-us/library/bb232045.aspx

When a message is sent to an external recipient, Exchange 2010 will always select a single connector through which to send the message. The selected connector must meet the message size constraints. After Exchange 2010 has eliminated all connectors whose message size restrictions are less than the size of the message being routed, routing applies the following criteria to determine which connector it will select:

1. From the list of all the connectors configured in the Exchange organization, Exchange narrows the list to connectors that satisfy all the following criteria:

   • In the scope for the local server

   • Enabled

   • With an address space that matches the recipient's e-mail domain

2. From the resulting list, Exchange selects the connector with the most specific address space match.

If more than one connector meets the address space match criteria, Exchange 2010 routing evaluates the following criteria to select a connector:

1. Connector cost   The cost of the connector is the sum of the cost assigned to all the IP site links between the source Active Directory site and the Active Directory site that contains the source servers for the connector, and the cost assigned to the connector. The connector with the lowest aggregate cost is selected. If more than one connector has the same cost, the selection process continues to the next step.

2. Proximity   The source server that has the closest proximity to the routing server is selected. This means that the local server is chosen over another Hub Transport server in the same Active Directory site, and a server in the local Active Directory site is chosen over a source server in a remote Active Directory site. If more than one connector matches the criteria, the selection process continues to the next step.

3. Alphanumerically lower connector name   If more than one routing path has the same cost and proximity, the connector with the name that has the lowest alphanumeric value is selected.

I am looking for an out of the box native way to complete this. I have seen people say they create a script that triggers a change to the send connector based on an event such as device response or such. I have also seen a response regarding using MX records in a way to provide this. I haven't been able to wrap my head around the use of the MX records yet.

Still looking for any other options that may be out there.

Hi ExchGuy13,

Thank you for your question.

By my understanding, we could refer to the following steps to troubleshoot:

1. We just configure the connect with MX, then we send test email;
2. If the email  is still in queue, we could check the configuration by the following link, then we can enable smarthost to test.

https://technet.microsoft.com/en-us/library/aa997285(v=exchg.141).aspx

  3. If email was sent to external, we could configure the same value of send connector, then we could configure the different Proximity; then we could test message flow. If there are same Proximity; we could configure different the name of send connector, it will be distinguished by Alphanumerically lower connector name.

We could refer to the following links:

https://social.technet.microsoft.com/Forums/exchange/en-US/fbb3319b-c3f5-4da8-ac5f-f7ebb9aefd7f/exchange-2010-send-connector-failover-automatic-or-manual?forum=exchange2010

https://social.technet.microsoft.com/Forums/exchange/en-US/ff796350-2044-413b-9345-c50980d21918/fault-tolerant-feature-of-exchange-2010-smtp-connector?forum=exchange2010

If there are any questions regarding this issue, please be free to let me know. 

Best Regard,

Jim