SHARED SMTP DOMAIN CONFIGURATION<\/strong><\/h2>\n\n\n\nWith both the Corporate and Subsidiary operating their own on-premises Exchange Server systems, the ability to have both Corporate and Subsidiary users sending as the \u2018global_brand.com<\/em>\u2019 SMTP domain is possible. At a high level, one procedure to configure a shared SMTP domain between on-premises Exchange Server systems is the following:<\/p>\n\n\n\n\n- Configure \u2018global_brand.com\u2019<\/em> as an Accepted Domain<\/a> in both the Corporate and Subsidiary on-premises Exchange Server systems.<\/li>\n\n\n\n
- Assign a \u2018global_brand.com<\/em>\u2019 Primary Email Address (Reply-To address) to the mailboxes homed on both Corporate and Subsidiary on-premises Exchange Server systems.<\/li>\n\n\n\n
- Assign an additional \u2018sub_brand.com<\/em>\u2019 email address (proxy address<\/a>) to the mailboxes in Subsidiary.<\/li>\n\n\n\n
- Utilise Corporate as the first-hop system for all inbound messages being delivered to \u2018global_brand.com\u2019 <\/em>email addresses.<\/li>\n\n\n\n
- Utilise Corporate as the relay system for all messages destined for a Subsidiary mailbox.<\/li>\n\n\n\n
- Create Contact objects in Corporate which represents each Subsidiary mailbox.<\/li>\n\n\n\n
- For each Contact object, set the Primary Email Address (Reply-To address) to the \u2018global_brand.com<\/em>\u2019 email address.<\/li>\n\n\n\n
- For each Contact object, set the forwarding address (ExternalEmailAddress<\/a>) to the \u2018sub_brand.com<\/em>\u2019 email address.<\/li>\n\n\n\n
- Create an SMTP Send Connector<\/a> from the Corporate source servers to the Subsidiary destination servers to route messages to Subsidiary recipients using the \u2018sub_brand.com<\/em>\u2019 email address.<\/li>\n<\/ol>\n\n\n\n
Based on the above step-by-step process, the following diagram shows the path an externally generated email message sent to Subsidiary user Bob would follow.<\/p>\n\n\n\n
\n- Message addressed to Subsidiary user Bob using his \u2018bob@global_brand.com<\/em>\u2019<\/a> email address.<\/li>\n\n\n\n
- Message flows through the Corporate<\/a> message hygiene system.<\/li>\n\n\n\n
- Message is delivered to the Corporate Exchange Server system.<\/li>\n\n\n\n
- The Corporate Exchange Server does not find a local mailbox for Bob, however, does find Bob\u2019s contact object.<\/li>\n\n\n\n
- The Corporate Exchange Server relays the message to the Subsidiary Exchange Server system using Bob\u2019s \u2018bob@sub_brand.com<\/em>\u2019<\/a> forwarding email address.<\/li>\n\n\n\n
- The message is delivered to Bob\u2019s mailbox.<\/li>\n<\/ol>\n\n\n\n
![\"\"](\"https:\/\/www.insentragroup.com\/nz\/wp-content\/uploads\/sites\/18\/2022\/11\/image.png\" "\\"\\"")
<\/figure>\n\n\n\nThe flexibility of sharing a common SMTP domain across on-premises Exchange Server systems does not exist within the Microsoft 365 (M365) cloud. With M365, a tenant is the logical boundary for security, policy and administration, thus an SMTP domain can only be activated in a single tenant.<\/p>\n\n\n\n
Note: Although Microsoft does have SMTP domain sharing on their roadmap (Feature ID: 67161: Exchange: Microsoft 365 cross-tenant SMTP domain sharing in private preview<\/em>), it is still in development.<\/p>\n\n\n\nBefore we explore the brand configuration options available to the Subsidiary for their move to M365, let us summarise what we know:<\/p>\n\n\n\n
\n- The Corporate on-premises Exchange Server system has \u2018global_brand.com<\/em>\u2019 configured as an Accepted Domain.<\/li>\n\n\n\n
- The Subsidiary on-premises Exchange Server system has \u2018global_brand.com<\/em>\u2019 configured as an Accepted Domain.<\/li>\n\n\n\n
- Corporate mailboxes are using the \u2018global_brand.com<\/em>\u2019 SMTP domain as their Primary Email Address (Reply-To address).<\/li>\n\n\n\n
- Subsidiary mailboxes are using the \u2018global_brand.com<\/em>\u2019 SMTP domain as their Primary Email Address (Reply-To address).<\/li>\n\n\n\n
- Microsoft does not allow the same SMTP domain (i.e., \u2018global_brand.com<\/em>\u2019) to be activated in multiple disparate tenants.<\/li>\n\n\n\n
- The \u2018global_brand.com<\/em>\u2019 SMTP domain will be a registered domain in the Corporate M365 tenant thus, the \u2018global_brand.com<\/em>\u2019 SMTP domain cannot<\/em><\/strong> be activated in the Subsidiary M365 tenant.<\/li>\n<\/ul>\n\n\n\n
To move an on-premises Subsidiary mailbox to M365 using the hybrid mailbox move<\/a> process, the \u2018global_brand.com<\/em>\u2019 email address must be stripped from the Subsidiary mailbox since it is not an active domain in the Subsidiary M365 tenant (Troubleshoot migration issues in Exchange hybrid – Exchange | Microsoft Docs<\/a>). Accordingly, if the Subsidiary moves to their own M365 tenant, Subsidiary users’ Primary Email Addresses (Reply-To addresses) would need to change from \u2018global_brand.com<\/em>\u2019 to \u2018sub_brand.com<\/em>\u2019. Thus, all messages sent from the Subsidiary mailboxes will be branded with the \u2018sub_brand.com<\/em>\u2019 SMTP domain.<\/p>\n\n\n\nOPTIONS FOR RESOLUTION:<\/strong><\/h2>\n\n\n\nBefore the Subsidiary can migrate their mailboxes to M365, a decision must be made by the Corporate and Subsidiary on brand relevancy and how Subsidiary branding will be managed going forward. The options available to the Subsidiary are as follows:<\/p>\n\n\n\n
\n- Migrate Subsidiary mailboxes into the Corporate M365 tenant. This option allows Subsidiary to retain their existing brand, \u2018global_brand.com<\/em>\u2019 and maintain their existing Client experience.<\/li>\n\n\n\n
- Rebrand Subsidiary to \u2018sub_brand.com<\/em>\u2019 and migrate Subsidiary mailboxes to Subsidiary M365 tenant. All future messages will be sent using the \u2018sub_brand.com<\/em>\u2019 SMTP domain. This option requires the Subsidiary communicate their brand change to their Clients<\/a>.<\/li>\n\n\n\n
- Rebrand Subsidiary to \u2018sub_brand.com<\/em>\u2019 and migrate Subsidiary mailboxes to Subsidiary M365 tenant. Additionally, subscribe Subsidiary to an Address Rewrite service offered through a third-party provider. All inbound and outbound email sent to or from the Subsidiary messaging environment would need to be routed through the Address Rewrite service. The Address Rewrite service would replace the \u2018sub_brand.com<\/em>\u2019 domain with the \u2018global_brand.com<\/em>\u2019 for messages sent from the Subsidiary users. This option allows Subsidiary to maintain their existing Client experience.<\/li>\n<\/ul>\n\n\n\n
For organisations operating like Corporate and Subsidiary, it is important to remember you cannot configure multiple Office 365 tenants<\/a> with the same SMTP domain. This restriction forces entities like Subsidiary to either merge with Corporate, rebrand or implement some advanced configuration like Address Rewrite.<\/p>\n\n\n\nUnfortunately, this does bring us to the end of this blog insight. I hope you found it useful. If you would like to request any further information, please contact us<\/a>. You can also learn more about planning for tenant migrations in this article Microsoft 365 Tenant Migration Planning:<\/a> Part 1.<\/p>\n","protected":false},"excerpt":{"rendered":"The flexibility of sharing a common SMTP domain across on-premises Exchange Server systems does not exist within the Microsoft 365 (M365) cloud.<\/p>\n","protected":false},"author":117,"featured_media":15604,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"content-type":"","footnotes":""},"categories":[22],"tags":[],"class_list":["post-15603","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-migrations","entry"],"_links":{"self":[{"href":"https:\/\/www.insentragroup.com\/au\/wp-json\/wp\/v2\/posts\/15603","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.insentragroup.com\/au\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.insentragroup.com\/au\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.insentragroup.com\/au\/wp-json\/wp\/v2\/users\/117"}],"replies":[{"embeddable":true,"href":"https:\/\/www.insentragroup.com\/au\/wp-json\/wp\/v2\/comments?post=15603"}],"version-history":[{"count":0,"href":"https:\/\/www.insentragroup.com\/au\/wp-json\/wp\/v2\/posts\/15603\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.insentragroup.com\/au\/wp-json\/wp\/v2\/media\/15604"}],"wp:attachment":[{"href":"https:\/\/www.insentragroup.com\/au\/wp-json\/wp\/v2\/media?parent=15603"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.insentragroup.com\/au\/wp-json\/wp\/v2\/categories?post=15603"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.insentragroup.com\/au\/wp-json\/wp\/v2\/tags?post=15603"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
- \n
- Configure \u2018global_brand.com\u2019<\/em> as an Accepted Domain<\/a> in both the Corporate and Subsidiary on-premises Exchange Server systems.<\/li>\n\n\n\n
- Assign a \u2018global_brand.com<\/em>\u2019 Primary Email Address (Reply-To address) to the mailboxes homed on both Corporate and Subsidiary on-premises Exchange Server systems.<\/li>\n\n\n\n
- Assign an additional \u2018sub_brand.com<\/em>\u2019 email address (proxy address<\/a>) to the mailboxes in Subsidiary.<\/li>\n\n\n\n
- Utilise Corporate as the first-hop system for all inbound messages being delivered to \u2018global_brand.com\u2019 <\/em>email addresses.<\/li>\n\n\n\n
- Utilise Corporate as the relay system for all messages destined for a Subsidiary mailbox.<\/li>\n\n\n\n
- Create Contact objects in Corporate which represents each Subsidiary mailbox.<\/li>\n\n\n\n
- For each Contact object, set the Primary Email Address (Reply-To address) to the \u2018global_brand.com<\/em>\u2019 email address.<\/li>\n\n\n\n
- For each Contact object, set the forwarding address (ExternalEmailAddress<\/a>) to the \u2018sub_brand.com<\/em>\u2019 email address.<\/li>\n\n\n\n
- Create an SMTP Send Connector<\/a> from the Corporate source servers to the Subsidiary destination servers to route messages to Subsidiary recipients using the \u2018sub_brand.com<\/em>\u2019 email address.<\/li>\n<\/ol>\n\n\n\n
Based on the above step-by-step process, the following diagram shows the path an externally generated email message sent to Subsidiary user Bob would follow.<\/p>\n\n\n\n
- \n
- Message addressed to Subsidiary user Bob using his \u2018bob@global_brand.com<\/em>\u2019<\/a> email address.<\/li>\n\n\n\n
- Message flows through the Corporate<\/a> message hygiene system.<\/li>\n\n\n\n
- Message is delivered to the Corporate Exchange Server system.<\/li>\n\n\n\n
- The Corporate Exchange Server does not find a local mailbox for Bob, however, does find Bob\u2019s contact object.<\/li>\n\n\n\n
- The Corporate Exchange Server relays the message to the Subsidiary Exchange Server system using Bob\u2019s \u2018bob@sub_brand.com<\/em>\u2019<\/a> forwarding email address.<\/li>\n\n\n\n
- The message is delivered to Bob\u2019s mailbox.<\/li>\n<\/ol>\n\n\n\n
<\/figure>\n\n\n\nThe flexibility of sharing a common SMTP domain across on-premises Exchange Server systems does not exist within the Microsoft 365 (M365) cloud. With M365, a tenant is the logical boundary for security, policy and administration, thus an SMTP domain can only be activated in a single tenant.<\/p>\n\n\n\n
Note: Although Microsoft does have SMTP domain sharing on their roadmap (Feature ID: 67161: Exchange: Microsoft 365 cross-tenant SMTP domain sharing in private preview<\/em>), it is still in development.<\/p>\n\n\n\n
Before we explore the brand configuration options available to the Subsidiary for their move to M365, let us summarise what we know:<\/p>\n\n\n\n
- \n
- The Corporate on-premises Exchange Server system has \u2018global_brand.com<\/em>\u2019 configured as an Accepted Domain.<\/li>\n\n\n\n
- The Subsidiary on-premises Exchange Server system has \u2018global_brand.com<\/em>\u2019 configured as an Accepted Domain.<\/li>\n\n\n\n
- Corporate mailboxes are using the \u2018global_brand.com<\/em>\u2019 SMTP domain as their Primary Email Address (Reply-To address).<\/li>\n\n\n\n
- Subsidiary mailboxes are using the \u2018global_brand.com<\/em>\u2019 SMTP domain as their Primary Email Address (Reply-To address).<\/li>\n\n\n\n
- Microsoft does not allow the same SMTP domain (i.e., \u2018global_brand.com<\/em>\u2019) to be activated in multiple disparate tenants.<\/li>\n\n\n\n
- The \u2018global_brand.com<\/em>\u2019 SMTP domain will be a registered domain in the Corporate M365 tenant thus, the \u2018global_brand.com<\/em>\u2019 SMTP domain cannot<\/em><\/strong> be activated in the Subsidiary M365 tenant.<\/li>\n<\/ul>\n\n\n\n
To move an on-premises Subsidiary mailbox to M365 using the hybrid mailbox move<\/a> process, the \u2018global_brand.com<\/em>\u2019 email address must be stripped from the Subsidiary mailbox since it is not an active domain in the Subsidiary M365 tenant (Troubleshoot migration issues in Exchange hybrid – Exchange | Microsoft Docs<\/a>). Accordingly, if the Subsidiary moves to their own M365 tenant, Subsidiary users’ Primary Email Addresses (Reply-To addresses) would need to change from \u2018global_brand.com<\/em>\u2019 to \u2018sub_brand.com<\/em>\u2019. Thus, all messages sent from the Subsidiary mailboxes will be branded with the \u2018sub_brand.com<\/em>\u2019 SMTP domain.<\/p>\n\n\n\n
OPTIONS FOR RESOLUTION:<\/strong><\/h2>\n\n\n\n
Before the Subsidiary can migrate their mailboxes to M365, a decision must be made by the Corporate and Subsidiary on brand relevancy and how Subsidiary branding will be managed going forward. The options available to the Subsidiary are as follows:<\/p>\n\n\n\n
- \n
- Migrate Subsidiary mailboxes into the Corporate M365 tenant. This option allows Subsidiary to retain their existing brand, \u2018global_brand.com<\/em>\u2019 and maintain their existing Client experience.<\/li>\n\n\n\n
- Rebrand Subsidiary to \u2018sub_brand.com<\/em>\u2019 and migrate Subsidiary mailboxes to Subsidiary M365 tenant. All future messages will be sent using the \u2018sub_brand.com<\/em>\u2019 SMTP domain. This option requires the Subsidiary communicate their brand change to their Clients<\/a>.<\/li>\n\n\n\n
- Rebrand Subsidiary to \u2018sub_brand.com<\/em>\u2019 and migrate Subsidiary mailboxes to Subsidiary M365 tenant. Additionally, subscribe Subsidiary to an Address Rewrite service offered through a third-party provider. All inbound and outbound email sent to or from the Subsidiary messaging environment would need to be routed through the Address Rewrite service. The Address Rewrite service would replace the \u2018sub_brand.com<\/em>\u2019 domain with the \u2018global_brand.com<\/em>\u2019 for messages sent from the Subsidiary users. This option allows Subsidiary to maintain their existing Client experience.<\/li>\n<\/ul>\n\n\n\n
For organisations operating like Corporate and Subsidiary, it is important to remember you cannot configure multiple Office 365 tenants<\/a> with the same SMTP domain. This restriction forces entities like Subsidiary to either merge with Corporate, rebrand or implement some advanced configuration like Address Rewrite.<\/p>\n\n\n\n
Unfortunately, this does bring us to the end of this blog insight. I hope you found it useful. If you would like to request any further information, please contact us<\/a>. You can also learn more about planning for tenant migrations in this article Microsoft 365 Tenant Migration Planning:<\/a> Part 1.<\/p>\n","protected":false},"excerpt":{"rendered":"
The flexibility of sharing a common SMTP domain across on-premises Exchange Server systems does not exist within the Microsoft 365 (M365) cloud.<\/p>\n","protected":false},"author":117,"featured_media":15604,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"content-type":"","footnotes":""},"categories":[22],"tags":[],"class_list":["post-15603","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-migrations","entry"],"_links":{"self":[{"href":"https:\/\/www.insentragroup.com\/au\/wp-json\/wp\/v2\/posts\/15603","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.insentragroup.com\/au\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.insentragroup.com\/au\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.insentragroup.com\/au\/wp-json\/wp\/v2\/users\/117"}],"replies":[{"embeddable":true,"href":"https:\/\/www.insentragroup.com\/au\/wp-json\/wp\/v2\/comments?post=15603"}],"version-history":[{"count":0,"href":"https:\/\/www.insentragroup.com\/au\/wp-json\/wp\/v2\/posts\/15603\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.insentragroup.com\/au\/wp-json\/wp\/v2\/media\/15604"}],"wp:attachment":[{"href":"https:\/\/www.insentragroup.com\/au\/wp-json\/wp\/v2\/media?parent=15603"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.insentragroup.com\/au\/wp-json\/wp\/v2\/categories?post=15603"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.insentragroup.com\/au\/wp-json\/wp\/v2\/tags?post=15603"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
- Rebrand Subsidiary to \u2018sub_brand.com<\/em>\u2019 and migrate Subsidiary mailboxes to Subsidiary M365 tenant. All future messages will be sent using the \u2018sub_brand.com<\/em>\u2019 SMTP domain. This option requires the Subsidiary communicate their brand change to their Clients<\/a>.<\/li>\n\n\n\n
- The Subsidiary on-premises Exchange Server system has \u2018global_brand.com<\/em>\u2019 configured as an Accepted Domain.<\/li>\n\n\n\n
- Message flows through the Corporate<\/a> message hygiene system.<\/li>\n\n\n\n
- Assign a \u2018global_brand.com<\/em>\u2019 Primary Email Address (Reply-To address) to the mailboxes homed on both Corporate and Subsidiary on-premises Exchange Server systems.<\/li>\n\n\n\n