Migrate Fastmail to Microsoft 365: Step-by-Step Guide

Businesses that want to migrate Fastmail to Microsoft 365 face many hurdles. Lack of a direct bridge is the most severe. Admins can’t just ask the users to forward the emails and be done with it.

Moreover, this is not just a change of email service provider but a complete transformation of a business’s digital infrastructure. As an IT administrator, it is your job to prevent mistakes that can jeopardize your organization’s email communication.

Don’t worry, you are not alone; we are here to guide you every step of the way. We will tell you about the methods that work, what to use, and what to avoid. Let’s start off with the export-import method.

Export Import Route to Transfer Emails from Fastmail to O365

The Basic idea is that you use Fastmail’s export feature to get all your data in a local repository. However, you cannot use the emails you downloaded directly as they are not in the pure EML format but rather in a compressed folder format.

That’s why an intermediary step is to unzip the files to get the EML content we need.

In the last phase of our plan, we will use the import EML feature of the new Outlook for Desktop client to add all those Fastmail conversations into the Office 365 account.

Also Read: Conduct Qmail to Microsoft 365 Migration

Now that we know the plan, let’s execute it and migrate Fastmail to Microsoft 365.

• Start by logging in to your Fastmail account.
• Open Settings → Migration.
• Switch to the Export tab.
• Click the New mail export button.
• Fastmail allows you to select one specific folder (singular) at a time and apply a date filter on the email data present inside.
• Use these features to make the export more precise.
• Once your export is ready, click on Download to receive the data.

Save it on your computer, then use any free utilities to unpack the data.

Add and Migrate Fastmail to a Microsoft 365 Account

Now you have two options: either export all the data first and then Import, or Export one batch > import it, and repeat for the remaining data.

To import, we will use the new client; the classic client does not allow EML import, and when you drag and drop the emails to a folder, the preview can’t process the emails.

Drag and drop works somewhat for the New client. Although when you do this, Outlook blocks the full data from getting visible and gives a reason that says “this sender is not in your Safe Sender list,” so check out how to whitelist all emails in Outlook 365 to view the full message.

That’s why it is better to use the default mechanism, which is:

Settings > File > Import > Import button

Browse for the parent File > Choose the account from the list (only available in desktop client) > Select folder > Import.

However, this is a slow and error-prone process. As it is entirely up to the user how much time they take to complete the drag and drop, plus the amount of time they spend correcting mistakes.

Create App Password to Migrate Fastmail to Microsoft 365

Before you proceed, make one final check to verify that all the accounts you want to switch are using the IMAP protocol.

Note: Basic Fastmail plan doesn’t give you IMAP access; So you either have to upgrade the plan or use the export-import route.

You can find IMAP setup instructions on the Settings → Migration screen.

To set up Fastmail in the Outlook client, you would first have to enable 2FA for Fastmail and generate a custom app password.

Doing this will allow you to migrate Fastmail to Microsoft 365 with ease.

• Sign in to your Fastmail account.
• Under Settings → go to Privacy & Security.
• Look for the Connected apps & API tokens tab → then select Manage app passwords and Access.
• Tap on New app password (You will be prompted to “Verify it’s you” again → Use your actual password → Continue)
• If you do not see Outlook in the dropdown list, select Custom… and type in “Outlook”
• Then, you have to pick what Fastmail data the Outlook client gets access to. Keep the default settings and continue.
• Finally, press the Generate Password button.

A new page will open that contains the app password. Copy this password into a temporary Notepad. Don’t press Done unless you verify that everything is working.

Steps to Add the Fastmail Account to Outlook 365 Client

Now, hop on to the Outlook Client.

Depending on which version of Outlook you are using, the steps vary slightly. Don’t worry, we will cover both the new and classic editions. Note: You cannot use the Web app to set up your Fastmail account. Although it is possible to add Fastmail to the mobile app version of Outlook, we won’t be using it as there is no means to transfer data across accounts on the mobile version.

Classic Client

• If this is your first time using the classic client, then Outlook shows an open/enter your email address screen. Use this opportunity to put in your Fastmail ID. If you already have some accounts on Outlook, you won’t see this screen.
• Instead, go to File > Add Account.
  Enter your Email and use your App password instead of the real password. Click Connect.
• This prompts Outlook to do a Connection test, after which you should see a “Account successfully added” text.
• It won’t show up if any mistakes were made in any of the fields. Moreover, if Outlook fails to detect the server settings automatically, you can manually toggle the Advanced setup screen and type in your Fastmail server settings yourself.
• • IMAP imap.fastmail.com Port 993
  • POP pop.fastmail.com Port 995 (Don’t Use This)
  • SMTP smtp.fastmail.com Port 465 (SSL) or 587 (STARTTLS)

Use New Outlook Client and Transfer Fastmail to Office 365

• Click on the Settings cog at the top right.
• By Default, you are on the Accounts > Your Accounts path. Click on the Add Account button.
• Type your Fastmail email address.
• Under the Password field, copy and paste the app password we made earlier.
• Click on Continue.
• Let Outlook finish up all the tests and set up a connection.

If done correctly, you should see the Fastmail data slowly load up on the client.

Similarly, add your Office 365 Business/Microsoft 365 Enterprise account on the same Outlook client.

Once you are done, create a new folder on the Office 365 account to keep all the Fastmail data. It is not a good idea to mix all your emails, especially if you were already using the O365 account before the transfer.

Then all that is left is to drag and drop emails from the Fastmail account into your O365 account.

Problems with Manual Way to Migrate Fastmail to Microsoft 365

The lack of a centralized, admin-controlled export option means IT admins have to delegate the work to users.

Plus, the Export feature of the Fastmail service is severely limited. You can only export data from one folder at a time.

So, if you select a parent folder that does not have any emails itself but is a container for multiple child folders, your export will fail.

The one folder at a time condition is strict and applies to all Fastmail subscription tiers.

As of now, there is no way to bypass it, and the lack of a publicly available future feature roadmap makes it impossible to determine if any changes will happen that remove this limitation.

You may think that if “I migrate Fastmail to Microsoft 365 by making a copy of all my emails and putting them inside a single folder, and then exporting, it should work, right?”

Wrong; this is because you don’t know about another major roadblock. There is a strict 4GB cap for each export on the Fastmail client.

Most modern email communication exceeds that limit in a few months of continuous conversations.

Fastmail offers a 6 GB mailbox size in the basic plan, which expands up to 150 GB total storage per user in its Professional tier.

This means if a Professional user has fully utilized all the available space and wants to get all of the data out, they will have to do thirty-eight separate exports (38 x 4 GB = 152  GB).

Even the basic version requires 2 export cycles to pull out all the data from the 6GB mailbox.

Not only is the limit too small, but Fastmail also does not warn you about the incomplete export. It simply truncates the export midway. It is up to the user to determine what data has been exported and what is remaining.

Moreover, there is no official documentation explaining how the export works. It is not known whether Fasmail starts picking the older emails first and works its way to the newest, or vice versa.

You have to manually open up each zip and check the last email, then redo the export for the remaining items.

Precautions to Take While Shifting Emails from FastMail to O365 Manually

You might have more than one O365 account on your Outlook client. So, before you use the import facility, be sure to double-check that you are importing the data into the right account. Otherwise

However won’t face this problem if you use the Outlook webmail, as there you can only log in to one account at a time.

Although Fastmail UI shows the size of each individual, it does not show an aggregate value when you select more than one. So you have to guess or calculate manually.

One way to avoid hitting the size limits is to make a new parent folder in your Fastmail account called, To-Be-Exported. Inside of which you must have subfolders that each correspond to a particular set of mail. None of those subfolders should exceed the 4GB limit.

Fastmail emails have a fixed size of 70 MB. This does not mean that all messages will be 70 MB. However, it tells us that some messages can contain that much data. Our Destination Office 365 can handle messages of up to 150 MB, so depositing Fastmail data should not be a problem. However, admins first make a check to see if the limit is extended or not, as the default limit is 25 MB (a lot lower than what you would expect from Fastmail)

So you should increase the per-user O365 mailbox size and message limit before the transfer.

Professional Alternative to User-Level Transfers

If admins want to make sure that their Fastmail to O365 transfer goes smoothly, they should choose the SysTools IMAP to Office Migration tool. This solution is built from the ground up to tackle these scenarios. All you need is the user’s app password. And then the tool can handle the rest on its own.

You get real-time tracking on how many accounts have been processed and hw much data from each account has been transferred. Moreover, unlike the native export, this tool has no strict upper cap on how much data you can transfer over a single migration scenario.

So use it and do the entire transfer in one go. Here is the list of steps you need to follow:

Step 1. Download the tool and select IMAP as the source and Microsoft 365 as the destination. On the same setup page, mark the email workload and apply the Date filter.

Step 2. Choose others from the dropdown list and fill in the IMAP server details. Validate and press Next.

Step 3. Likewise, add your M365 admin account address and App ID, validate both, and press Next.

Step 4. On the User mapping screen, download the Template, fill in the User IDs + their app passwords, and import this CSV back into the tool.

Step 5. On the user preview screen, make the box next to their names, prioritize the most critical accounts, then validate and start migration.

Conclusion

In this blog, you saw various ways to migrate Fastmail to Microsoft 365. You can export all the data and import it via the Outlook client. Set up both of your accounts and transfer via your cursor. The problem with both of these methods is that they rely on the user themselves. Which results in inconsistencies and a lot of troubleshooting requests. What we suggest instead is to use a Professional tool that provides a single control and coordination center for the migration.