How to (auto) compress attachments in messages in Outlook?

Author: Kelly Last Modified: 2025-03-04

Large attachments can cause sending and receiving delays, slow down Outlook, and inflate mailbox size, making email management frustrating. While manually deleting attachments is an option, it’s time-consuming and can lead to the loss of important files. To prevent these issues, compressing attachments is a smart solution. It reduces file size, speeds up email delivery, and helps Outlook perform more efficiently. This guide introduces three methods to compress attachments in Outlook.

Manually compress attachments before sending (Basic & Time-Consuming)

Batch compress attachments in selected emails with Kutools for Outlook 👍 (Fast & Efficient)

Automatically compress attachments in all incoming emails with Kutools for Outlook 👍 (Smart & Fully Automated)

Manually compress attachments before sending

Since Outlook does not have a built-in compression feature, you can manually zip files before attaching them to emails.

Step 1: Compress files before attaching

Locate the files you want to send via email. Right-click the selected files and choose Send to > Compressed (zipped) folder.

the screenshot of step about sending compressed attachments with manually compressing files firstly 1

Step 2: Attach the compressed file to an email

1. Right-click the compressed file and select Send to > Mail recipient.

the screenshot of step about sending compressed attachments with manually compressing files firstly 2

2. A new email window will open with the zipped file attached.

the screenshot of step about sending compressed attachments with manually compressing files firstly 3

Limitations:

❌ Manual process: Requires manually compressing files each time before attaching them.
❌ Limited to the outgoing emails: Only helps when sending attachments; does not reduce mailbox size or manage received emails.
❌ No automatic compression: If you forget to compress the files, they will be sent in their original large size.

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Auto Detach Feature in Kutools for Outlook

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Batch compress attachments in selected emails with Kutools for Outlook 👍

If you need to compress attachments in received emails to save storage space, Kutools for Outlook provides a one-click solution to batch compress all attachments in selected messages.

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Step 1: Select multiple emails

In the Mail view, select the emails whose attachments you want to compress.

Hold Ctrl to select multiple non-adjacent emails.
Hold Shift to select a range of adjacent emails.

Step 2: Apply batch compression

1. Click Kutools Plus > Attachment Tools > Compress All.

shot of the Compress All feature

2. In the 'Compress Settings' dialog, check 'Compress all attachments', then click OK.

shot of the Compress Settings dialog

Step 3: Confirm compression

1. A Compress All confirmation dialog box will appear. Click Yes to proceed.

shot of the Compress All confirmation dialog box

2. A Kutools for Outlook notification will show the number of attachments successfully compressed.

shot of the Kutools for Outlook notification

Advantages:

✅ Quick & effortless: Compresses multiple attachments with a single click.
✅ Reduces Outlook mailbox size: Saves storage without deleting attachments.
✅ Improves email performance: Helps Outlook run faster and reduces loading time.

Note: To apply the 'Compress All' utility of Kutools for Outlook, firstly, you should download and install Kutools for Outlook.

Automatically compress attachments in all incoming emails with Kutools for Outlook 👍

Even after reducing outgoing attachment sizes, large incoming attachments can slow down Outlook and clutter your mailbox. Kutools for Outlook offers an Auto Compress Attachments feature that automatically compresses all received attachments, eliminating manual work.

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Step 1: Enable the Auto Compress feature

Click Kutools Plus > Auto Compress > Enable.

shot of the Auto Compress feature

Step 2: Configure auto-compression settings

1. In the 'Auto Compress Attachments' dialog box, check 'Auto compress all received attachments'.

2. Under 'The file extension after compressing', select your preferred compression format.

3. Click OK to apply the settings.

shot of the Auto Compress Attachments dialog box

Result:

From now on, all incoming attachments will be automatically compressed, reducing mailbox size and improving email performance—without requiring any manual effort.

Advantages:

✅ Fully automated: Compresses attachments in real-time with no manual action required.
✅ Optimizes mailbox storage: Keeps Outlook running smoothly by reducing file sizes.
✅ Works on all incoming emails: Ensures that attachments do not clog your inbox.

Note: To apply the 'Auto Compress' utility of Kutools for Outlook, firstly, you should download and install Kutools for Outlook.

Which Method Should You Choose?

Here’s a comparison of the three methods to help you decide which one best suits your needs:

Method	Best For	Ease of Use	Effectiveness	Automation
Manually Compress Before Sending	Occasional users who don’t mind manual steps	⭐⭐⭐	⭐	❌ No
Batch Compress Attachments in Selected Emails	Users who frequently receive large attachments	⭐⭐⭐⭐	⭐⭐⭐⭐	❌ No
Auto-Compress Incoming Attachments	Users who want a fully automated solution	⭐⭐⭐⭐⭐	⭐⭐⭐⭐⭐	✅ Yes

By choosing the right method, you can enhance Outlook’s performance, reduce email size, and keep your mailbox running smoothly! 🚀

Demo: (Auto) compress attachments in messages in Outlook

Discover the Kutools / Kutools Plus tab in this video, added by Kutools for Outlook. Now, most features, including AI functionalities, are free! Pro features come with a 30-day trial without limitations!