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Monday, June 17, 2024

How to Configure Cross forest connectors (Mail flow) Exchange 2010 to Exchange 2013


Source Domain – CareExchange.in

Target Domain – TargetExchange.in


Lets say CareExchange.in is migrating mailboxes across forest to TargetExchange.in

For Exchange TestUser@CareExchange.in  is migrated from CareExchange.in to TargetExchange.in

But still the administrator looks for a solution that TestUser has to receive email of “CareExchange.in” , Until the migration gets over completely. (As Mx Record will be changed only in the end of the migration)

Its kind of setting up cross forest coexistence mail flow between Exchange 2010 and Exchange 2013 Forest.


This process only should be done . when the migration is going to happen for a short period of time . Cause the domain CareExchange.in will be set to internal relay in both the forests . The disadvantage of this process is , if some one sends a email where user doesn’t exist – User wont get a NDR.

If you wish to over come it . We need to introduce an another domain. and set forwarder in the source and internal relay is set only on the target domain . Am not going to go deep about it  , in this post.


Configuring Accepted Domains  –

First Make Sure – The Domain is Set to Internal Relay (In Source Domain – CareExchange.in)

Organization Configuration – Hub Transport – Accepted Domains – Right Click Properties


And Login to Target Domain – TargetExchange.in

Organization Configuration – Hub Transport – Accepted Domains – Right Click New Accepted Domain

Create a Internal-Relay domain


Configuring Send Connector on the Source Domain (CareExchange.in) –

Note : (CareExchange.in) Email Hits the Source Server . Searches for the user ,

When User Exists , Email is delivered

When user does not exist , Send the email to the target domain .

When User does not exist on source and destination domain , there is NO NDR Gets generated

So try to Have this solution for a short period of time.

Login to Exchange 2010 Server – (Domain – CareExchange.in)

Organization Configuration – Hub Transport – Connectors – New Send Connector

Name  – Cross Forest Connector

Intented Use – Custom


Address – CareExchange.in (SourceDomain)

Cost – 1

(If you already have a connector with Cost 1 – No problem , Please continue)


Choose – Route Email Through the following smart hosts

Enter the  Destination Exchange Server 2013 IP address.

Make Sure IP is pinging and reachable



Choose Authentication is None

If you wish to use TLS , Follow the below link




Now Send Connector is Configured on the source Domain,


Note – If you have SPF Records you should add it as SPAM filter may block while you send from Target domain to source domain

Do add your_domain.com, TXT, “v=spf1 MX:your_smtp_server_name ip4: ~all”


Create a Send Connector from Target 2013 to Source as we did in Exchange 2010

Satheshwaran Manoharan
Satheshwaran Manoharanhttps://www.azure365pro.com
Award-winning Technology Leader with a wealth of experience running large teams and diversified industry exposure in cloud computing. From shipping lines to rolling stocks.In-depth expertise in driving cloud adoption strategies and modernizing systems to cloud native. Specialized in Microsoft Cloud, DevOps, and Microsoft 365 Stack and conducted numerous successful projects worldwide. Also, Acting as a Technical Advisor for various start-ups.

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    • MX —> Source will forward will user not exist to target.
      Partial Migrated Users —> Target will forward if user not exist to source.

  1. In this scenerio, Let say if the email address is not exist in either envirnoment.Email will loop right?
    By default it will loop for 30 times and then generate NDR.Do I need to create a transport rule using X-Loop Header Right?

  2. cool article 🙂 Thanks Satheshwaran Manoharan. Kindly include configuration on test email accounts sending intra-forest and from outside the two domains.


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