Resolving “Sent Items” Duplication (Outlook/Gmail)

When using Microsoft Outlook configured with a Gmail or Google Workspace account via IMAP, every outgoing message can appear twice in your “Sent” folder. This issue litters your local client with duplicate items and wastes local disk space.

Quick Answer

Gmail automatically places a copy of every message sent through its SMTP server into the [Gmail]/Sent Mail folder. Duplicate entries appear when Microsoft Outlook is also configured to save a copy to its own local Sent Items folder. To fix this, uncheck “Do not save copies of sent items” or uncheck “Save copies of messages in the Sent Items folder” in Outlook.

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What Causes the Duplication?

Traditional IMAP servers are passive storage repositories: they do not know when an email is dispatched through an external SMTP server. As a result, email clients like Outlook manually upload a copy of every sent message to the server’s designated “Sent” folder via an IMAP APPEND command.

Gmail works differently. When you transmit an email using smtp.gmail.com, Google’s outgoing mail transfer agent (MTA) automatically creates a copy of the outgoing message, applies the system label [Gmail]/Sent Mail, and indexes it in your account automatically.

When Outlook is left at its default settings, two things happen:

1. Gmail’s Automatic Ingestion: Gmail sends the email and automatically adds a copy to the server-side Sent folder.
2. Outlook’s IMAP Append: Outlook uploads its own local copy to the sent folder over IMAP.

Both messages end up with different internal IDs (UIDs), so Outlook treats them as distinct emails and displays two identical entries in your sent view.

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Diagnostic Checklist: Where Does the Duplicate Originate?

Duplicate Sent Items
│
├── Open Gmail in a web browser (mail.google.com).
│   ├── Do you see duplicates in the web interface?
│   │   ├── YES ──► Two independent clients or an automated rule is sending duplicates.
│   │   └── NO  ──► Outlook-specific display issue. Proceed to Step 1 below.

If the web interface displays only one sent message, the duplicate exists solely within Outlook’s local .ost cache file. If the web interface also shows two sent emails, an add-in, CRM tool, or external SMTP relay is submitting the message twice.

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Step-by-Step Fixes for Microsoft Outlook

The steps to resolve this depend on your version of Microsoft Outlook.

Solution 1: Disable “Save Copies of Sent Items” (Outlook Classic / Windows)

For Outlook 2016, 2019, 2021, and Microsoft 365 desktop apps:

1. Open Outlook and click File in the top-left corner.
2. Select Options, then click Mail in the left sidebar.
3. Scroll down to the Save messages section.
4. Locate the option: Save copies of messages in the Sent Items folder.
5. Uncheck this checkbox.
6. Click OK and restart Outlook.

Note: If you have multiple email accounts in Outlook (such as an Exchange account alongside Gmail), unchecking this global setting stops Outlook from saving sent items for all accounts. If you require sent-item saving for an Exchange mailbox, use Solution 2 instead.

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Solution 2: Change Advanced Account Settings (Per-Account Basis)

If you manage multiple accounts in Outlook, disable saving copies specifically for your Gmail profile:

1. In Outlook, click File > Account Settings > Account Settings.
2. Select your Gmail IMAP account from the list and click Change.
3. In the account setup window, click More Settings in the bottom-right corner.
4. Go to the Advanced tab.
5. Under the Folders or Sent Items section, select:“Do not save copies of sent items” (or select Delete items from the server before closing Outlook depending on your build).
6. Click Apply, then OK, and complete the wizard.

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Solution 3: Re-map Gmail IMAP Folders (Prevent Folder Duplication)

Sometimes duplicates appear because Outlook creates a local “Sent Items” folder that runs parallel to Gmail’s official [Gmail]/Sent Mail folder.

1. Open Gmail in a web browser and go to Settings > Labels.
2. Make sure Sent Mail has Show in IMAP checked.
3. Open Outlook, right-click the root folder of your Gmail account, and select IMAP Folders….
4. Click Query, select the redundant “Sent” or “Sent Items” folder (not [Gmail]/Sent Mail), and click Unsubscribe.

If your Gmail IMAP folders are completely out of sync, or if folder indexing is causing Outlook to freeze, see Why Gmail IMAP is Stuck on “Syncing Subscribed Folders”.