Gmail – How to insert an Excel sheet as part of a new mail message

There are two ways to insert an image in the body of the mail:

• drag-and-drop it from its folder to the desired position in the message (depending on your browser, it might or might not work);
• enable the Insert image feature from the mail settings and click on the Insert image button (this option requires that the email is composed using Rich formatting).
  ← new look ← old look

To enable "Insert image":

1. Go to Settings
2. Click on the Labs tab
3. Search for Inserting images feature
   
4. Click on the Enable option
5. Click Save Changes at the bottom of the page

It's based on a initiative called Schema.org. Google announced this feature for Gmail in May 2013: http://gmailblog.blogspot.dk/2013/05/take-action-right-from-inbox.html

Quotes from the post (emphasis and linkifying mine):

Email is an important part of how we get things done -- from planning an event with friends to organizing that family vacation to Costa Rica. And today, getting those things done is getting a little easier with new quick action buttons in Gmail, designed to help you tackle your digital to-do’s as quickly as possible.

... and ...

These buttons appear next to certain types of messages in your inbox and let you take action on an email without ever having to open it. For example, you can RSVP to your friend's party invitation or rate that restaurant you went to last night all right from the inbox. You’ll be checking things off that to-do list in no time.

... and ...

If you are a developer and want to add actions to your emails, check out http://developers.google.com/gmail/schemas to learn more.