How to Backup and Export Outlook Autocomplete Nicknames from Microsoft 365

You know when you start typing someone's name in the "To" field and Outlook automatically suggests their email address? That's not coming from your Contacts. That's coming from a hidden file called the nickname cache — and if you lose it, those suggestions are gone forever.

Microsoft quietly builds this list in the background every time you send an email. Over years of use, it becomes incredibly valuable — containing hundreds or thousands of email addresses for people you've contacted but never formally saved as contacts. Vendors, clients, one-time collaborators, that guy from accounting whose last name you can never remember.

The problem? This hidden file is notoriously difficult to access and backup. It's not in your Contacts folder. You can't export it from Outlook. And if you migrate to a new Microsoft 365 tenant, switch computers, or have any mailbox issues — it's gone. Users are left manually typing email addresses they haven't typed in years, desperately trying to remember "was it john.smith@ or jsmith@?"

What is the Outlook Nickname Cache?

Let's be clear about what we're talking about:

This is NOT your Contacts folder. Your Contacts are the people you deliberately saved — with phone numbers, addresses, and other details. You can see them, edit them, export them easily.

The nickname cache is different. It's a hidden list that Outlook builds automatically every time you send an email. Type "bob@" and hit send? Bob's email is now in your nickname cache. You never saved him as a contact, but next time you type "bob", Outlook will suggest him.

Over years of emailing, this hidden cache grows to include:

• Everyone you've ever emailed — whether you saved them or not
• One-time contacts — That vendor from 2019, the contractor who did one project
• Spelling variations — "Mike Smith" vs "Michael Smith" at the same address
• Group addresses — Distribution lists you've used

For someone who's used Outlook for 5+ years, this cache often contains 500 to 2,000+ email addresses. Most of them were never saved to Contacts. They only exist in this hidden file.

And here's the painful part: You don't realize how much you rely on it until it's gone. Then you're staring at a blank "To" field, trying to remember email addresses you haven't manually typed in years.

Why Backup Outlook Autocomplete Data?

There are several critical scenarios where backing up nickname data is essential:

1. Microsoft 365 Tenant Migrations

Moving users to a new Microsoft 365 tenant? The autocomplete cache does not migrate automatically. Without a backup, users lose years of accumulated email suggestions and have to rebuild them manually.

2. Mailbox Moves and Hybrid Migrations

When moving from on-premises Exchange to Exchange Online (or vice versa), autocomplete data can be lost or corrupted. A backup ensures you can restore it.

3. User Offboarding and Compliance

Need to preserve a departing employee's contact relationships? The autocomplete cache shows everyone they've ever emailed — valuable for compliance, legal holds, or handoff to a replacement.

4. Disaster Recovery

If a mailbox is accidentally deleted or corrupted, having a backup of the autocomplete data means users don't lose their accumulated suggestions.

5. New Device Setup

Setting up Outlook on a new computer? While Microsoft 365 syncs autocomplete data, having an export lets you verify nothing was lost.

Where is Nickname Data Stored in Microsoft 365?

In older versions of Outlook (2007 and earlier), the autocomplete cache was stored locally in an .nk2 file on the user's computer. If that file was deleted or the user got a new computer, the suggestions were gone.

In Microsoft 365 and Exchange Online, the autocomplete cache is stored server-side as a hidden message in the user's mailbox. This means:

• Suggestions sync across devices automatically
• There's no local .nk2 file to backup
• You need special tools to access and export this data

The cache is stored in a hidden folder called Suggested Contacts within the mailbox. Standard Outlook export tools don't include this data — which is why you need a specialized backup tool.

How to Backup Nicknames with MSPTool

MSPTool's MS365 Nickname Backup utility connects to your Microsoft 365 tenant and exports autocomplete data from any mailbox. Here's how to use it:

Step 1: Connect Your Microsoft 365 Tenant

1. Go to portal.msptool.com and sign up or log in
2. Navigate to MS365 Utilities
3. Click Connect New Tenant
4. Sign in as a Global Administrator of the tenant you want to connect
5. Review and accept the permissions (read-only mailbox access)

Once connected, your tenant will appear in the list. The connection uses Microsoft's official OAuth flow — we never see or store your admin password.

Step 2: Run the Nickname Backup Utility

1. Click Run Utility on the Nickname Backup card
2. Select your connected tenant
3. Choose All mailboxes or Specific mailboxes
4. If specific, select the users you want to backup
5. Click Create Task

Step 3: Download Your Backup

The utility processes each mailbox and extracts the autocomplete cache. You can monitor progress in real-time. When complete:

• Download individual CSV files per mailbox
• Or download a combined ZIP file with all exports

Each CSV contains the display name, email address, and metadata for every autocomplete entry in that user's cache.

Single User vs. Organization-Wide Backup

Single User Backup

Need to backup just one person's autocomplete? Perfect for:

• Executive assistants managing a VIP's mailbox
• Users getting a new computer
• Troubleshooting autocomplete issues for one person

Select "Specific mailboxes" and choose just the user you need.

Organization-Wide Backup

Need to backup everyone? Select "All mailboxes" and the utility will process every user-mailbox in your tenant. This is ideal for:

• Pre-migration backups before moving to a new tenant
• Quarterly compliance snapshots
• Disaster recovery preparation

Large organizations can have hundreds of mailboxes processed in a single run, with individual CSV exports for each user.

Frequently Asked Questions

What permissions does the tool need?

MSPTool requests read-only access to mailbox data through Microsoft's standard admin consent flow. We use the Graph API and EWS (Exchange Web Services) to access the hidden autocomplete cache. We cannot send emails, delete data, or modify mailboxes.

How long does the backup take?

Each mailbox typically takes 10-30 seconds to process, depending on the size of the autocomplete cache. For a 100-user organization, expect roughly 20-50 minutes for a full backup.

What format is the export?

Exports are standard CSV files that can be opened in Excel, Google Sheets, or any spreadsheet application. Each row represents one autocomplete entry with columns for display name, email address, and type.

Can I restore the autocomplete data?

The CSV export serves as a backup and reference. Restoring autocomplete data to Exchange Online requires re-importing contacts or manually adding them. The export preserves all the information needed for restoration.

Is this the same as exporting contacts?

No. The autocomplete cache is separate from the Contacts folder. Many email addresses in autocomplete were never saved as contacts — they're just people the user has emailed. This tool specifically exports the autocomplete/nickname data, not the Contacts folder.

Does this work with shared mailboxes?

Yes. Shared mailboxes have their own autocomplete cache. Select the shared mailbox when running the utility.

What about on-premises Exchange?

Currently, MSPTool's Nickname Backup works with Microsoft 365 / Exchange Online. On-premises Exchange servers with hybrid connectivity may work — contact us to discuss your setup.

Conclusion

The Outlook autocomplete cache is one of those things users don't think about until it's gone. Then they realize how much they relied on it. By proactively backing up nickname data before migrations, device changes, or as part of regular disaster recovery, you save users from the frustration of rebuilding their email suggestions from scratch.

MSPTool's MS365 Nickname Backup makes this easy — connect your tenant, run the utility, and download your exports. Whether you need to backup one executive or your entire organization, it takes just a few clicks.