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3 Steps to Success: How to Plan an Office 365 Email Migration

In this blog post, we’ll outline the three essential steps you should take to plan an Office 365 email migration. Like most issues surrounding IT, these steps focus on identifying and mitigating risk so let’s first underline why email is so important.

Why email matters so much

emailFirst invented in the 1960s, email is now the very definition of a business-critical system. It’s often the primary communication method between colleagues, customers and suppliers. It’s used as a two-factor security login method for web apps and password resets and it’s also used as one of the most important aspects of any web-based process; written confirmations. Put plainly, being without email is simply not an option.

And don’t forget that your email archive is an extremely important part of your company’s trading record. It is good practice to keep your email archive for a minimum of 12 months, but you probably want to be thinking about archiving for at least six years. Email histories form vital evidence when dealing with HMRC inspections or contract disputes. You can’t afford to lose your archive.

But, isn’t migrating Office 365 Email Easy?

‘Ease of use’ is a key criterion in most purchase decisions. Its why Microsoft has invested so much in making its cloud-based applications – like Office 365 – seem easy. Log in, sign up and you’re up and running. Got stuck? A quick search on Microsoft, YouTube or Google will give you the answer. It’s no wonder so many small to medium-sized enterprises (SMEs) in the UK are migrating to Office 365. (50,000/month at the last count and so joining 60 million commercial entities across the globe who are already there).

Office 365 Stats

How hard can it be? Well, be warned. Email migration is not without its risks and, as email is considered a ‘business-critical’ system for most SMEs, its one you simply can’t afford to get wrong. You’d better get a plan.

How to Plan an Office 365 Email Migration

We break our planning down into three essential steps: what you’re migrating, the migration plan and executing the migration. This is an iterative process, which is why we call them steps.

How to Plan an Office 365 Email Migration Step 1: Know what you’re migrating

All successful projects begin with planning. With mail migrations, understanding what needs to be migrated or reconfigured is the first step. Consider the following checklist and you’ll quickly realise it’s quite a complex task.

  • User mailbox data which typically includes emails, contacts, calendars and tasks. These are your highest risk items because users make the most noise when things go wrong. You should plan your migration so that there is zero disruption to mailbox data. No downtime, no data loss, no disruption.
  • Application mailbox data or system mailboxes. If you use email to send out automated messages from things like an email marketing platform, CRM, ERP, MRP, Mobile App, web app or e-commerce platform, they will be affected by the migration too. They’re often overlooked by migration novices.
  • Shared mailboxes. It’s quite likely you use shared mailboxes for generic emails like info@ or for team emails like sales@. These are often used for web leads and general enquiries, so it’s important they work properly.
  • Distribution lists are used to send email to pre-defined lists and save a lot of time. If you’ve gone to the trouble of creating them in the first place, you don’t want to have to do it again!
  • DNS records will need to be reconfigured to that your email flows to Office 365 instead of your old system
  • User devices will also need to be reconfigured to connect to their new mailboxes in Office 365. This includes desktops, laptops, tablets and phones.

How to Plan an Office 365 Email Migration Step 2: Make and Share the Plan

Your email migration should complete with no downtime or data loss and minimal impact on your users. To say this takes a little planning is an understatement! For instance, your users may be spread across multiple locations and time zones and they will be using all sorts of different devices and email clients. You may also have different email domains hosted by different providers. So, your plan should include all of the following sub-plans.

A licensing plan

As part of the planning process, you’ll need to ‘map’ old emails onto your new Office 365 ‘tenant’ and confirm what you want to happen to each of the accounts. This is where licensing skills are needed. You can control your costs here by creating a ‘hybrid’ licensing set up. (We wrote about this topic in an earlier post. Click here if you want to read it).

User-by-user plan

An email migration gives you an ideal opportunity to tidy up your email. Regular users will normally migrate with the same username and password, but ex-employees’ mailboxes can be migrated to shared mailboxes which don’t require a separate license and can be accessed by a line manager. If you’ve got employees with multiple email addresses, we can consolidate them as part of the migration process.

From a security perspective, this migration exercise gives you an opportunity to review how many email accounts you have and to ask the question, ‘do we really need them all’? Remember the more email addresses you have, the more opportunities others have to try and breach your defences and cause you harm.

Spam and malware filtering plan

spam filteringYou’ll then need to work out what your spam and malware filtering plan will be so as to reduce spam and malware risk. If you’re already using a mail filtering service, it’s highly likely you can keep using it. But, Office 365 has three separate layers of anti-spam and anti-malware filtering built-in so most customers discard their current mail filtering service, reducing both cost and complexity.

Device clients plan

Your migration team should now catalogue the current device and mail client landscape and then make a plan for moving to new clients if necessary.

You can use a wide range of devices and mail clients to work with Office 365, so your users can probably keep using their same tools. Of course, they may wish to adopt Outlook, which comes bundled with most Office 365 licenses and now works well across all Windows, macOS, Android and iOS devices. (Remember Exchange Online works with Outlook 2010 and above, so if you have that already then you can keep using that).

devices office 365

We strongly recommend that you consider moving your entire team to the latest version of Outlook. It comes bundled, promotes collaboration and simplifies administration and there is now also a free webmail client for Office 365.

Team Resources Plan

Once you’ve created a plan for how to migrate between services, you need to work out who is going to do it. Whether your current set up is complicated or not, it pays to have a Microsoft Partner help you with the move. The level of resources required during the migration may be too much for the in-house team to go it alone. And although the in-house department knows your users the best and will identify any idiosyncrasies in the planning stages, they may simply not have the resources or expertise required to carry out this time-critical project without outside help.

Active Directory Plan

Finally, if you have an Active Directory Domain on-premise, you may wish to synchronise this with the Azure Active Directory that manages authentication for the Office 365 tenant so that users can continue to use their network log-on as the single source of identity. This should also form part of the overall migration plan and is typically implemented post-migration if required.

Now you know what you’re going to do and who’s going to do it, it’s time to share the plan with the senior management team, garner feedback and agree to timings. The two critical timings are the start date and the cut-over date. As a guide, a 200-user migration normally takes around four weeks to plan and execute.

How to Plan an Office 365 Email Migration Step 3: Executing the Plan

When the project starts, your users shouldn’t notice because all of the work will be happening in the background. Put simply, they should be able to carry on using their existing email like they always have. Then, at the cut-over point, they start using Office 365 instead. All of their email, calendar and contact items will have been copied across and will be up to date.

In the background, of course, a great deal of activity will be taking place and this includes the following: creating the Office 365 tenant, adding your domains, adding the chosen Office 365 licenses, creating the users, assigning the chosen licenses to them and copying the contents of their source mailbox into Office 365.

At the cut-over point, the DNS records are changed to make Office 365 the live email service for your migrating domains. This will then automatically connect Outlook on Windows machines to their new Office 365 account and perform another data sync. An hourly sweep carried out over the next 72 hours following cut-over will catch any emails that have been delivered to the old mailboxes and will copy them into the Office 365 ones.

Companies often choose to install other Office 365 products and services from their Office 365 at the same time. Typically, these might be SharePoint, OneDrive for Business and Skype for Business.

The secret to avoiding email fail

Migrating email to Office 365 might give the impression that data is being moved. In fact, the secret to a successful migration is that you move nothing. By all means copy data, but don’t move it. Back it up, back it up and back it up again because if the worst happens, you’ll always have copies of the data.

Remember, the old military saying ‘fail to prepare, prepare to fail’ is particularly relevant here. Go into a migration project unprepared and you’re almost guaranteed not just to lose data but suffer significant business disruption too. However well-resourced your in-house IT department is, at this point, they’ll become overwhelmed and costs will escalate as you throw more resources at the problem. Our advice (naturally!) is to get expert assistance. We can tell you how to plan an Office 365 migration, but knowing and doing are different things!

We’ll share some horror stories of migration plans that go wrong in our next post.


Find Out More

See our selection of our short video case studies featuring a few of our Office 365 and Azure clients. Good Microsoft licensing structuring is an important part of every migration or set up we complete.

If you would like to know more or talk to us about how Microsoft Office 365 might help your company, get in touch with us today.


A strategic thinker and planner with a flair for developing and implementing effective business strategy, Jon has spent the last seven years working closely with Microsoft in the cloud computing and business intelligence space.

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