When you add a URL to an email message in Outlook on the web, or when you receive a message with a URL in the body, you'll see a rich preview that includes a link title, thumbnail image, and description of the link. This is called a link preview.
With the Link Preview feature turned off, a URL looks like this: https://www.microsoft.com.
With Link Preview turned on, the same URL looks like this:
Note: Link Preview is turned on by default. If you don't see a link with a thumbnail image, title, and description like the one shown above and want to turn on Link Preview, contact your IT administrator.
Add a link preview
When composing an email message, type a URL in the message body. For example, you could type http://microsoft.com.
If Link Preview is turned on, it will automatically provide the site's name, description, and a thumbnail image (if available) in the message body.
Note: To open or follow a link preview, simply click it like any other hyperlink.
Turn off Link Preview
Link Preview is turned on by default. However, you can turn it off.
At the top of the page, select > Mail.
In the Options pane, under Mail > Layout, select Link preview.
Under Link preview, clear the Preview links in email check box to turn off Link Preview.
Select the Preview links in email check box to turn Link Preview back on.