Please do as follows to compress attachments of one or multiple emails in an email folder.

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1. Open an email folder and select one or multiple emails with attachments you want to compress at once.

2. Click Kutools > Compress All. See screenshot:

3. Then a Compress All dialog box pops up, click the Yes button.

Then all attached pictures and other attachments in the selected emails are compressed immediately.

For uncompressing all attached pictures and attachments which are compressed by our Compress All feature you are received from others, please do as follows.

1. Select one or multiple emails which have the compressed attachments.

2. Then click Kutools > Uncompress All. See screenshot:

3. In the Uncompress All dialog box, click the Yes button.

Then all compressed attached pictures and attachments in selected emails are uncompressed.

Note: This utility is only applied to the attachments which are compressed by our Compress All feature.

When sending or receiving emails with attachments attached, the Compress utility of Kutools for Outlook can help you auto compress them at once.

1. You need to enable the Auto Compress function by clicking Kutools > Options. See screenshot:

2. In the Attachment Options dialog box, under Compress tab, check Automatically compress outgoing attachments and Automatically compress receiving attachments options, and then click the Ok button. See screenshot:

After checking these two options, (you can also check one of them as you need) when you sending or receiving emails with attachments attached, the attachments will be compressed automatically in Outlook.

Notes:

1. You can also enable the Compress All and Uncompress All utility with selecting an attachment in email, when the Attachment Tools tab showing, click Kutools > Compress All / Uncompress All. But this compress all and uncompress all can only work in current selected email.

2. If picture attachments are not compressed, you can configure as follows: click Kutools >Options to open the Attachment Options dialog box; in the dialog box, check the Handle picture attachments option under General tab, and then click the Ok button.

3. Under the Compress tab of the Attachment options dialog box, you can also configure to specify file extensions for all compressed attachments. See screenshot below:

4. Under the Compress tab of the Attachment options dialog box, you can also set compression exclusion based on attachment file extensions or attachment size. See screenshot below: