Domain Coexistence
Mergers and acquisitions are often accompanied by the unification of brands and corporate identities, including the consolidation of email addresses. However, the transition from source to target tenant might take considerable time. On Demand Migration offers domain coexistence services to close this gap, allowing your employees to send mail from new addresses and access cross-tenant data before the migration is finished. The following services are currently available on the account migration dashboard:
- Address Rewrite Service seamlessly changes the source users' email flow as if they're already fully migrated to the target tenant. Outgoing email addresses are replaced with the recipient's email address in the target tenant, while all incoming mail is automatically redirected to the source mailbox. Address rewriting can be started once the account is matched or migrated, giving you time to prepare and migrate mailboxes. The Address Rewrite Service requires additional licensing.
- Calendar Sharing allows users from the source and target tenants to see each other's free or busy information.
Address Rewrite Service
The Address Rewrite Service substitutes the From, To, and Cc addresses in the outgoing emails with the addresses from the target or source tenant depending on the selected address rewriting scenario. Emails are automatically redirected to the source or target mailbox. You can specify the users processed by the service. For example, you can turn on the service for only Sales and Marketing team members.
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IMPORTANT: Address Rewrite Service requires additional licensing. The service only works with accounts that have been matched in the target tenant. See matching accounts for more information. Mailbox provisioning is not required. |
Address Rewrite Service Message Flow
Address Rewrite Service is intended for creating a coexistence space for domains in which all the email messages coming from the source or target mail domain will look like they were sent from the unified mail domain according to the selected settings. The Address Rewrite Service will take all the necessary steps to create this coexistence space in the Exchange online environment, including creating and managing all the required connectors, mail flow rules, mail-enabled users, and groups in source and target environments. The administrator should add or remove source mail users to this coexistence space and activate or deactivate the Address Rewrite Service.
The mail message flow in a unified domain with an activated Address Rewrite Service is as described below:
Unified mail domain in the source tenant
- When a user sends an email as user@target.domain mail user, it is redirected to the Address Rewrite Service server if it is addressed to external recipients.
- When the Address Rewrite Service receives an email from user@target.domain, it checks user eligibility to for the address rewriting service and then processes the email by rewriting @target.domain to @source.domain for every user address that is found in the coexistence space. The addresses in "From", "To" and "Cc" fields of the email message are rewritten for all external recipients. Then Address Rewrite Service passes the processed email message to the source Exchange Online. Internal recipients that reside in the source receive this email message with unchanged addresses.
- Exchange Online at the source sends a message to external recipients as if it was sent by a user from @source.domain, and all addresses of users added to coexistence scope in From, To and Cc are rewritten for external recipients.
- The External recipient is not aware about @target.domain and replies (or create a new email) to the user@source.domain
- When the reply or a new mail arrives to the source mail domain it will be forwarded to the target. Target recipient gets the message as if it was forwarded from the Exchange online at the source from user@source.domain
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If the message...
Is sent outside the organization from a member of the coexistence group
Do the following...
Route the message using the connector Quest Coexistence Connector Outbound.
Except if...
Sender IP address belongs to one of Mail Relay IP addresses. |
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If the message...
Is sent outside the organization and is received by a member of the coexistence group specified in the To or CC field
Do the following...
Route the message using the connector Quest Coexistence Connector Outbound.
Except if...
Sender IP address belongs to one of Mail Relay IP addresses. |
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Mail flow scenario
From: Mail Relay Servers
To: Microsoft 365
How to identify email sent from Mail Relay Servers
Identify incoming messages from Mail Relay Servers by verifying that the sending server's IP address is within Mail Relay IP address ranges and the sender's email address is an accepted domain in your organization. |
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Mail flow scenario
From: Microsoft 365
To: Mail Relay Servers
When to use the connector
Use only when there is a transport rule (Quest Coexistence Rule From and Quest Coexistence Rule ToCc) is set up that redirects messages to this connector. Routing method Route email messages through Mail Relay Servers. |
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Mail flow scenario
From: Mail Relay Servers
To: Microsoft 365
How to identify email sent from Mail Relay Servers
Identify incoming messages from Mail Relay Servers by verifying that the sending server's IP address is within Mail Relay IP address ranges and the sender's email address is an accepted domain in your organization. |
Unified mail domain in the target tenant
- When a user sends an email as user@source.domain it is redirected to Address Rewrite Service server if it is addressed to external recipients.
- When the Address Rewrite Service receives email from user@source.domain, its checks user eligibility for the address rewriting service and then processes it by rewriting @source.domain to @target.domain for every user found in the coexistence space. The addresses in "From", "To" and "Cc" of the email message are rewritten for all external recipients. Then Address Rewrite Service passes the processed email message to the target Exchange Online. Internal recipients that reside in the source receive this email message with unchanged addresses.
- Exchange Online at the target sends the message to external recipients as if it was sent by user@target.domain, and all addresses of the users added to the coexistence scope in "From", "To" and "Cc" are rewritten for external recipients.
- External recipient is not aware about @sourcedomain and replies (or create a new email) to user@target.domain.
- When the reply or a new mail arrives to the target mail domain it will be forwarded to the source. Source recipient gets the message as if it was forwarded from the target Exchange online from user@target.domain
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If the message...
Is sent outside the organization from a member of the coexistence group
Do the following...
Route the message using the connector Quest Coexistence Connector Outbound.
Except if...
Sender IP address belongs to one of Mail Relay IP addresses. |
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If the message...
Is sent outside the organization and is received by a member of the coexistence group specified in the To or CC field
Do the following...
Route the message using the connector Quest Coexistence Connector Outbound.
Except if...
Sender IP address belongs to one of Mail Relay IP addresses. |
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Mail flow scenario
From: Microsoft 365
To: Mail Relay Servers
When to use the connector
Use only when there is a transport rule (Quest Coexistence Rule From and Quest Coexistence Rule ToCc) is set up that redirects messages to this connector. Routing method Route email messages through Mail Relay Servers. |
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Mail flow scenario
From: Mail Relay Servers
To: Microsoft 365
How to identify email sent from Mail Relay Servers
Identify incoming messages from Mail Relay Servers by verifying that the sending server's IP address is within Mail Relay IP address ranges and the sender's email address is an accepted domain in your organization. |
| |
Mail flow scenario
From: Mail Relay Servers
To: Microsoft 365
How to identify email sent from Mail Relay Servers
Identify incoming messages from Mail Relay Servers by verifying that the sending server's IP address is within Mail Relay IP address ranges and the sender's email address is an accepted domain in your organization. |
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TIP: If Exchange Server Integration fails, click Try to fix and Quest will try to help you resolve the issue. |
Using the Address Rewrite Service requires following steps:
Address Rewrite Service Considerations
Each customer has a dedicated environment and inbound IP address for Address Rewrite Service.
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Caution: Do not edit or remove the groups, connectors and rules related to Address Rewrite Service otherwise the service may fail. These rules can be removed manually only if address rewriting no longer needed. |
The following groups, connectors and rules appear in Exchange Admin Centers after Exchange Server Integration is configured depending on which rewrite direction is chosen:
Rewrite Senders’ Address to Target
On source tenant:
- Quest On Demand Coexistence group contains accounts (recipients) joined to Address Rewriting
- Inbound Quest Coexistence Connector helps control mail flow for Address Rewrite Service from Microsoft 365 to the organization
- Outbound Quest Coexistence Connector helps control mail flow for Address Rewrite Service from the organization to Microsoft 365
- Quest Coexistence Rules implement Address Rewriting messaging policy for accounts joined to Address Rewriting
On target tenant:
- Quest Coexistence Connector helps control flow of email messages for Address Rewrite Service from the organization to Microsoft 365
Rewrite Senders’ Address to Source
On source tenant:
- Quest Coexistence Connector helps control flow of email messages for Address Rewrite Service from the organization to Microsoft 365
On target tenant:
- Quest On Demand Coexistence group contains accounts (recipients) joined to Address Rewriting
- Inbound Quest Coexistence Connector helps control mail flow for Address Rewrite Service from Microsoft 365 to the organization
- Outbound Quest Coexistence Connector helps control mail flow for Address Rewrite Service from the organization to Microsoft 365
- Quest Coexistence Rules implement Address Rewriting messaging policy for accounts joined to Address Rewriting
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NOTE:
The service only works with accounts that have pairs in the target tenant. You should match or migrate an account before adding it to address rewriting.
In case an email is sent to a group of people, including a migrated user, that email is automatically forwarded to the migrated user, and then if the migrated user clicks Reply all, he / she gets a copy of his / her reply message. This is default behavior. |
Address Rewriting Scenarios
Address Rewriting supports the following scenarios:
- Replace senders’ address with the target primary email address.
- Replace senders’ address with the source primary email address.
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NOTE:
- The address is only rewritten in the mail that goes to the recipients outside your organization. Internal users receive the mail with the original address. Microsoft
- M365 Advanced Threat Protection default settings may cause issues with the Address Rewriting Service. Please ensure that "Automatic forwarding" is set to "On" in the "Outbound spam filter policy" for your source or target tenant depending on the rewriting scenario you choose.
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Rewriting senders’ address to the target address
Use case: users from the source tenant need to communicate with external recipients from the name of the target organization. It usually happens when the mail migration is not yet finished, but you want to use the consistent branding.
To rewrite senders’ address to ones from the target select To target for the Rewrite senders’ address to on the Domain Coexistence widget. You cannot change this setting after Address Rewrite Service is provisioned.
Check Senders' Address property on the Mailboxes tab to find the effective email address after rewriting. If the account don't have the Exchange mailbox provisioned in the target tenant (mail user), the target primary SMTP address is used for address rewriting.
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IMPORTANT: We recommend that all incoming mail is automatically redirected to the source mailbox. Set Mail Flow for the mailbox to To source. |
Rewriting senders’ address to the source address
Use case: migrated users need to communicate with external recipients from the name of the source organization. It usually happens when you need to keep the original brand while merging all accounts in the target tenant.
To rewrite senders’ address to ones from the source select To source for the Rewrite senders’ address to on the Domain Coexistence widget. You cannot change this setting after Address Rewrite Service is provisioned.
Check Senders' Address property on the Mailboxes tab to find the effective email address after rewriting.
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IMPORTANT: We recommend that all incoming mail is automatically redirected to the target mailbox. Set Mail Flow for the mailbox to To target. |
