Migrate Intermedia to Office 365 Mailbox: A Complete Migration Guide

Can you migrate Intermedia to Office 365?

Yes, but the method decides what arrives. Microsoft’s IMAP batch handles data as follows:

Data type	Microsoft IMAP batch
Mail folders	Migrated
Calendars	Not migrated
Contacts and tasks	Not migrated
Items per mailbox	500,000, newest first
Message size	35 MB maximum

• The source mailboxes remain untouched, so a failed pass can be repeated.
• Example: a mailbox with 600,000 items migrates only its newest 500,000.

Why Does Intermedia to Office 365 Migration Fail?

When a user attempts to migrate Intermedia to Office 365, the migration process fails for certain reasons mentioned below.

• Mailboxes with more than 500,000 items lose their oldest messages.
• Messages above 35 MB are skipped by the batch.
• Restricted admin rights block full mailbox access.
• Incorrect CSV credentials fail the endpoint connection.
• Unprovisioned Microsoft 365 mailboxes stop the batch.

Events that Indicate a Failed Intermedia Migration

• The batch status reads “Completed with errors” for several users.
• Outlook shows fewer items than Intermedia webmail.
• The new mailbox contains no calendars or contacts.
• The migration report lists skipped items above 35 MB.
• The endpoint test returns a connection failure message.

Preparation Before You Migrate from Intermedia to Office 365

• Confirm with Intermedia which protocols your account permits.
• Create and license every Microsoft 365 mailbox first.
• Record each mailbox’s item count and largest message.
• Prepare a CSV with address, username, and password.
• Lower the MX record TTL several days before cutover.

How to Migrate Intermedia to Office 365?

The right method depends on mailbox count, item volume, and the access Intermedia grants. Microsoft’s native routes suit small, mail-only projects, while larger or mixed projects need a tool that does not inherit those limits.

Method 1: Microsoft IMAP Batch in Exchange Admin Center

How it works: Exchange Online signs in to each Intermedia mailbox over IMAP and copies the mail folders.

Sync: the batch repeats about every 24 hours until you complete it, so new mail keeps arriving.

1. Create and license each mailbox in the Microsoft 365 admin centre.
2. Open the Exchange admin centre, select Migration, and choose New batch.
3. Choose IMAP migration, then enter the Intermedia IMAP server, port 993, and SSL.
4. Upload the CSV containing address, username, and password.
5. Start the batch, review the report, and complete it before changing MX.

Limitation: every destination mailbox must exist and be licensed before the batch starts.

Method 2: Exchange Online PowerShell

How it works: the same IMAP rules apply, but you control endpoint settings.

Scale: Microsoft’s example sets 50 concurrent migrations and 25 concurrent incremental syncs.

1. Connect to Exchange Online PowerShell.
2. Test the IMAP connection to Intermedia.
3. Run New-MigrationEndpoint with the server, port 993, and SSL.
4. Create the batch with New-MigrationBatch and your CSV.
5. Run Start-MigrationBatch and monitor progress with Get-MigrationUser.

Limitation: every error still needs interpretation from migration reports.

Considerations Before Using Manual Methods

Before you move from Intermedia to Microsoft 365, it’s better to consider a few points and accordingly proceed with either of the options.

• IMAP batches carry mail folders only.
• Messages above 35 MB are skipped.
• Mailboxes migrate newest first and stop at 500,000 items.
• Hosts may withhold the admin rights that other methods require.

Method 3: Best Solution to Migrate Intermedia to Office 365

The Aryson IMAP Backup Software connects to each mailbox over IMAP, so it needs no endpoint, batch, or PowerShell. This software provides multiple login modes, such as admin and single-account login. At the same time, it lets users import mailboxes via a CSV import feature. That too, without affecting the folder structure and attachments. With the help of the same software, one can export IMAP to PST or PDF format. On top of that, the software comes with a demo version that lets users migrate 50 emails per folder.

1. Install the Aryson IMAP Backup Tool and run it as an administrator.
2. Select IMAP as the source and enter Intermedia details, or import a CSV.
3. Select Office 365 as the destination and sign in.
4. Preview folders, then apply a date range and remove duplicate filters.
5. Map the required mailboxes, and click Start Migration to transfer Intermedia to Office 365.

Once you follow the above steps, there will be no scope left for errors or data integrity issues. Still, it is recommended to read through the complete documentation of the software. This eventually leads to creating a better understanding of the software and helps you out with the further migration processes.

Comparison in a Glance: Manual Methods Vs Aryson

Method	Setup	Best for	Main limit
IMAP batch	Admin centre	Small projects	35 MB, 500,000 items
PowerShell	Scripts	Tuned batches	Scripting expertise
Aryson tool	Desktop	Bulk CSV migration	Test calendars first.

Why Choose Aryson for Intermedia Migration?

• CSV import can even migrate 99+ mailboxes in one run instead of repeated manual entries.
• This software can also migrate IMAP to Zoho Mail target=”_blank”, Office 365, Google Workspace & other clients.
• Date range filters split oversized mailboxes into smaller, verifiable passes.
• Folder preview catches wrong selections before any data moves, which avoids repeating a full pass.
• The demo migrates 50 emails per folder, which allows a safe pilot.

Conclusion

With changes in mailbox size, timeline, and contract dates, the ideal approach varies as well. Microsoft’s IMAP batch and PowerShell route handle small, mail-only projects. Both of them run into the 35 MB message limit and the 500,000-item ceiling when mailboxes are large. Eventually, these limits cause most failed batches, not just slow ones, because skipped items surface only after the batch report is reviewed. At the same time, we have the Aryson IMAP to Office 365 Migration Tool to migrate Intermedia to Office 365. You can even contact our technical support team to get personalised assistance during the migration, from CSV preparation to final verification in Outlook.

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