Outlook attachment preview tricks

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The Outlook preview pane isn’t just convenient, it’s a good front line defence against hackers and viruses.  Here’s an in-depth look at a deceptively simple part of Outlook.

The standard preview pane hasn’t changed a lot for many versions of Outlook.

Microsoft now calls it a Reading Pane which recognizes that many people read and respond to messages from the side-pane alone.  Despite the official rename, many people still call it a preview pane.  Old habits die hard.

Click on the attachment and Outlook switch from a preview of the email to previewing the attachment.

Click on ‘Back to message’ to switch between the attachment preview and the message itself.

The preview of Office documents works pretty well but can get messed up if the document has complex formatting.  That’s a combination of the previewer’s limitations and the narrow column for the preview pane.

You can preview another Outlook message that’s been forwarded or saved as an attachment.

The previewers are limited, sometimes too limited.  For example, the image previewer has no rotate or zoom options.

Outlook 2016’s image preview supports the JPG orientation flag unlike earlier Outlook releases. As you can see, that’s not always enough so some manual rotate options would be nice.


The main reason why the preview pane is considered ‘safe’ compared to opening the attachment is the ‘previewer’.  Previewers are plug-ins to Outlook that display a version of the attachment in the preview pane.  They are separate from the main program you’d use to view or edit those documents (like Word or Excel).

Previewers are mostly hidden to us because they are installed automatically with Office or with other products.  Office comes with previewers for Office file types plus the main image types, HTML files and plain text attachments.

The most common extra previewer is a PDF previewer which is installed as part of the Adobe Acrobat Reader.


There’s a security warning before using a preview filter for the first time: “You should only preview files from a trustworthy source”.  That’s just a precaution by Microsoft, really wording from MS Legal, disclaiming themselves from liability.

The message is NOT not the result of some virus test of that specific attachment nor a comment on that type of attachment generally.

We’re not aware of any cases of computer infection via the attachment preview windows in recent releases of Outlook.  We suggest UNchecking the “Always warn before previewing this type of file” to let attachment previews happen immediately.

The special previewer add-ins are listed and can turn them off at File | Options | Trust Center | Trust Center Settings | Attachment Handling.

If there’s no previewer available, Outlook will tell you.

Blocked attachments

Outlook blocks some attachments automatically according to the file extension.

The preview pane will alert you to a blocked attachment but there’s no direct option to bypass the block.

Previewing web links

The preview pane does NOT protect you from malicious web links.  These are links to web pages that will try to infect your computer via the browser.

Always hover your mouse over a link in an email or attachment.  Make sure the http  link matches the visible text and isn’t for some other web site.

Here’s a fake CNN message where the web link is to a totally unrelated site:

Clicking on a link in a previewed attachment will open your default browser.  The link action is controlled by your Windows settings, not Outlook and definitely not the sender.

Email preview only

Calendar and Contact Outlook items can have attachments too but, strangely, Outlook doesn’t support attachments in the preview/reading pane.

You have to double-click on an attachment to open it fully.

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