This guide is part of our M365 Migration Series.
Explore every step of the tenant-to-tenant migration journey below:
This blog is part of a series introducing you to the concepts around migrating to M365. This can be migrations from other platforms such as Google Workspace or other on-prem/cloud solutions, tenant-to-tenant migrations, or on-prem Exchange/SharePoint to Exchange Online/SharePoint Online.
For organizations undergoing complex transitions like those driven by IT Services Mergers and Acquisitions this process plays a key role in unifying systems and ensuring business continuity.
This process, at its core from a technology presepctivete, is actually pretty simple. You will spend a lot more time planning, defining migration waves, doing organization change management, and communicating to your clients than you will actually doing the technology part. This blog series will provide practical steps to help you with your journey and provide real-world examples of how it can be done. Some of the recommendations will follow Microsoft best-practice, while some will not. These blogs will also use Microsoft-native tools. Yes, this is possible and can work quite well using the native tools.
This blog is part of a series introducing you to the concepts around migrating to M365. This can be migrations from other platforms such as Google Workspace or other on-prem/cloud solutions, tenant-to-tenant migrations, or on-prem Exchange/SharePoint to Exchange Online/SharePoint Online.
This process, at its core from a technology presepctivete, is actually pretty simple. You will spend a lot more time planning, defining migration waves, doing organization change management, and communicating to your clients than you will actually doing the technology part. This blog series will provide practical steps to help you with your journey and provide real-world examples of how it can be done. Some of the recommendations will follow Microsoft best-practice, while some will not. These blogs will also use Microsoft-native tools. Yes, this is possible and can work quite well using the native tools.
Email Basics
When it comes to your mail migration, there are a few critical questions that you must ask. Getting these decided in the early planning stages is critical to success. Have these discussions early with your leadership and project team to make sure everyone is on the same page.
MX Record
This is probably the most critical decision. If your migration involves moving your MX record, you will want to decide when that moves and plan that move early in your planning stage.
Some questions you should ask:
- Is the MX record moving before any user cutovers or after they are all complete? I’ve seen it both ways, while most orgs move it last (and that’s what Microsoft recommends). However, depending on the skill sets of your team, you may consider moving it first, especially if this is a non-Exchange to Exchange migration, for instance Google Workspace to Exchange. Personally, I am a lot more comfortable with PowerShell and manipulating Exchange mailboxes than I am doing the same thing in Google Workspace. So, moving the MX records and controlling mail flow with forwards on mailboxes is a lot easier for me. You will put forwards in the old place or the new place, so when the MX record moves technically doesn’t matter. What changes is where the forwards go.
- What is the time-to-live (TTL) of the record in DNS? If this is longer than 15 minutes, you probably want to consider changing it prior to changing the MX record and then changing it back after the record is moved. This will ensure that globally, your record updates in a timely manner to make sure mail flows properly to your environment. If your normal TTL is 24 hours, for example, that is way too long for this. You should set it lower at least 24 hours in advance of making the MX record change, then set it back to 24 hours after the change is made.
- Who is responsible for making the change? This is likely your networking or security team, so coordinate with them well ahead of time. You’ll want to make this change is done during off hours, so make sure they are ready for that.
Migration Waves
Determine how your clients will move to M365. You don’t want to move everyone at once unless you are an extremely small organization. Move a small power user wave first, more so to make sure the system works. Some questions to ask during planning:
- How many waves do we want?
- I recommend starting with 1 extremely small wave, less than 5 accounts, to make sure the system works and the rules you have in place to move mail between the current system and M365 work.
- Next, I would move 15-20 accounts for more validation. Don’t be afraid to put a power user in this wave. If your CIO is adventurous, put them and their executive assistant in this wave. They will be your test for delegated mailboxes and calendars.
- Next, scale at whatever pace is comfortable for your organization. That could be 100 accounts per wave, 1,000 accounts, etc.
- How do users co-exist between the platforms? One important thing to remember is that while you’re in migration mode, calendars will not work very well, especially if your coming from a non-Exchange system. Keep that in mind as you plan waves. People that collaborate frequently should be in the same waves.
SharePoint
I will say it right from the top – if you’re coming from non-SharePoint to SharePoint Online, the migration is much more difficult than migrating email. There can be a steep learning curve for people that have never administered or used SharePoint before. It just has different constructs, behaves differently, and is structured differently than other on-prem and cloud storage platforms.
The most important thing during the planning phase is determining the structure of SharePoint. Some common questions you should ask:
- In what scenarios are you going to create additional sites? Having this outlined upfront will help you in conversations with clients.
- How are you going to separate “personal” data stored in your current system and “organizational” data? Personal data should be migrated to OneDrive for Business, while organizational data should be migrated to SharePoint. How are you going to determine what is what and where it should move.
- How are you going to define quotas for OneDrive and SharePoint sites? Set this, especially for OneDrive, before anyone gets access to the system if possible.
Security and Compliance
If you are using Defender and Purview, you will need to have some base-level configurations in place prior to moving any users into the platform. You want these in place for security and compliance purposes.
Defender
If you are sending mail directly to M365 instead of routing it through something else first (such as Proofpoint, Barracuda, etc.), you will be using Defender for your email security. You will need to have everything under Email & collaboration > Policies & rules > Threat Policies configured. These are:
- Anti-spam policies
- Anti-phishing policies
- Safe links
- Safe attachments
- Tenant Allow/Block List
Even if you route email through something else first, there is still a section here you should look at called Enhanced Filtering.
Purview
You should use Purview to configure retention settings at a minimum. This will apply to both Exchange and SharePoint. There is a lot more to Purview than just retention, but at a minimum, retention needs to be configured per your organization’s requirements prior to migrating data into the platform.
Lots of options exist for retention, such as retaining data for a set period and deleting it at the end of that time, with options for setting this based on created, modified, and last accessed date (last accessed date functionality expected to be released to GA in June 2026).
For enterprises consolidating multiple environments during IT Services Mergers and Acquisitions establishing consistent retention and compliance policies across tenants is a crucial step before any large-scale migration.
Final Thoughts
Migrating to Microsoft 365 is a journey that goes far beyond technical execution. Success hinges on thorough planning, clear communication, and a deep understanding of your organization’s needs. By addressing critical decisions early—such as MX record timing, migration wave structure, and SharePoint organization—you set the stage for a smooth transition. Equally important is preparing your security and compliance configurations to safeguard data and ensure regulatory alignment.
While challenges will arise, especially when moving from non-Microsoft platforms, leveraging native tools and best practices can make the process manageable and even rewarding. Ultimately, a well-planned migration not only modernizes your technology but also empowers your organization to collaborate and innovate more effectively in the cloud.
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