Email outages time in domain removal process from one M365 tenant and adding to other M365 Tenant

Question

Hi Team

We have migrated mailboxes from a domain called Domain A(Source M365 Tenant) into Domain B(Destination Tenant).

Please note:Domain A and Domain B both are in different M365 Tenant.

Next After Migration-

We are planning to remove domain A from Source -M365 and add Domain A to my MS 365 Tenant(Destination)

1.Movement of Domain A to Destination MS365 tenant is to retain the domain name and be able to use the smtp(Alias)  mask on the mailboxes migrated into Domain B.

2. we wish to keep receiving emails in this process with no outage/or minimal email outage time.

Do we have any emails outage time in this process?

Any changes in dns pre-removal activities?

how to minimal dns activites replication time from source tenant to destination tenant.

Answer 1

Hi @TA.Saurabh.Singh ，

Do we have any emails outage time in this process?

Noticed that the mailboxes have already been migrated to the target tenant, then how about the DNS records like MX? If the DNS records of the source tenant hasn't been changed to point to the target tenant, yes, you will have emails outage time during the process, and this is inevitable as I know.

Any changes in dns pre-removal activities?

Before removing the domain from the source tenant, you'll need to ensure all DNS records that point to domain A in the Source tenant, such as MX and TXT are pointed to the target tenant.

how to minimal dns activites replication time from source tenant to destination tenant.

Normally, the best practice is to prepare the domain and DNS records prior to migrating the mailboxes. Anyways, you can still follow the guidance and adapt them to your scenario. Basically, the tasks aiming at minimizing the outage time involve 1. Begin domain verification process on target tenant in advance to allow the DNS record time to propagate as it can take up to 72 hours; 2. In DNS, change the TTL value on the MX record for the primary email domain you wish to transfer to a small number.

More details, you can go through the official document below:

How to migrate mailboxes from one Microsoft 365 or Office 365 organization to another

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