Migrate Multiple Email Accounts to Office 365 or Microsoft 365

Microsoft 365 (formerly Office 365), also known as Exchange Online, provides a cloud-based email solution for small, medium, and large enterprises. While the adoption is in the early stages, organizations—especially SMEs—are increasingly leaning towards Office 365 as it is more cost-effective when it comes to data security, backups, disaster recovery, and scalability.

There are multiple ways to migrate email accounts and mailboxes from various email servers to Office 365. Based on the mail server or technology you are using for hosting your email services, you can choose the technique to move mailboxes and migrate email accounts from your existing email systems or clients, such as Outlook, to Office 365.

Methods to Migrate Multiple Email Accounts to Office 365 or Microsoft 365

There are different methods to migrate email accounts from your existing email servers to Office 365. Below we have briefly discussed these methods with their risks and limitations.

Migrate Email Accounts to Office 365 using PST Import Method

Microsoft 365 or Office 365 supports PST files, which Outlook uses to store mail items on the local drive. Outlook creates PST for POP email accounts. For IMAP, Exchange, Office 365, and Outlook.com accounts, Outlook creates OST files. However, users can export their mailboxes in Outlook to PST files using the Outlook Import Export wizard.

If the Microsoft Outlook client is being used in your organization, you can ask your users to export their mailboxes to PST files using the Outlook Import Export wizard and share the exported PST files with you. Once you have all the PST files, you can create a PST import job and a PST to Office 365 mailbox mapping file (.csv) to upload and import PST files into Office 365.

You can choose between the Network Upload and Drive Shipping methods for migrating PST files to Office 365.

In the Network Upload method, you need to upload the PST files to the Azure Cloud Storage using AzCopy tool before you can map and import the PST files to user mailboxes on Office 365.

In the Drive Shipping method, you need to ship the PST files in a BitLocker-encrypted drive to one of Microsoft's data centers before you can map and start the PST import job.

For detailed steps, you can refer to this article.

Migrate Email Accounts to Office 365 using IMAP Migration

You can use the IMAP migration method to migrate email accounts and mailboxes from all types of IMAP-enabled email servers. The IMAP migration option is available in Office 365 admin center that you can use to migrate the contents of mailboxes to Office 365.

However, before you choose this migration method to move the email accounts to Office 365, you must know its limitations:

• With IMAP Migration, you can only move the Inbox and other mail folders from IMAP systems to Office 365. Other mail items, such as contacts, tasks, calendar items, etc., are not migrated. 
• You can migrate up to 500,000 mail items from the user's mailbox. The emails are migrated in descending order (newest to oldest).
• Any mail item more than 35 MB in size is skipped. Therefore, you won't find these emails on the destination Office 365 mailbox.

Besides these limitations, IMAP migration requires you to have access to user mailboxes. As an administrator if you know the passwords, you can create a CSV file containing users' email IDs, usernames, and passwords to move their accounts to Office 365. However, if you don't know the passwords, you may have to reset the passwords, which can impact users.

If the users don't know the new password, they won't be able to access or use their email account during or after the mailbox migration. Thus, you must communicate the changes to the users and let them know how the migration will affect them.

Conclusion

When migrating email accounts from existing email systems or infrastructure to Office 365 or Microsoft 365 with the manual methods and approaches, you may encounter several challenges. These can also have an impact on user access, leading to downtime. However, you can avoid such situations and automate the mailbox migration from Outlook clients configured in your current email systems to Office 365 by using a third-party solution, such as Stellar Migrator for Outlook. The software can directly migrate PST files containing user mailbox items to the destination Office 365 tenant in a few clicks with complete integrity and precision. All you need to do is select the PST file and enter the user credentials to export the PST to the Office 365 user’s mailbox with Microsoft Modern Authentication.