With the Moosend Campaign Editor you can enable the Google Promotion Settings in order to annotate you email in the Gmail Promotion tab. According to Google, email annotations allow you to bring life to your messages by using images, discount codes, expiration dates and more!
Let's see how you can enable this setting:
1. Click on the Settings button. 
2. Then, scroll down and click on the Google Promotion Setting option to expand the menu.
3. Check the the checkbox Enable Promotion Annotation to enable the setting.
4. Click on the Promotion Image to upload an image for your annotation. You can upload an image from your computer, or directly from various other sources, such as Facebook, Instagram, Dropbox and many more!
Once you add your image, a new Remove button will appear. If you want to remove your image, click on this button.
The image for your annotation will appear here:
5. Click on the Sender Avatar to upload an image that will appear as your sender's logo. You can upload an image from your computer, or directly from various other sources, such as Facebook, Instagram, Dropbox and many more!
The image for your sender's avatar will appear here:
6. Set a Description for your annotation. 
The Description for your annotation will appear here:
7. Set a Discount Code for your offer within the annotation. 
The Discount Code for your offer within the annotation will appear here:
8. Click on the Expiration Date to set an Expiration Date for your offer in your annotation.
A calendar appears.
9. Click on the blue buttons to navigate between months.
A warning will appear if you try to navigate to a date before the current one.
10. Click on a date to select when your offer will expire.
11. Select the Time page, to set the exact time on that date when your offer will expire. Drag the Hours and Minutes sliders to set the exact time of day. 
12. Click on the Save button when you're done.
The Description for your annotation will appear here:
13. Click on the Preview button to preview your design.
14. Click on the G button to to preview your annotation.
In case you have already added a Product into your design and selected to Use it for Gmail Promotions Tab, the description will be auto-filled in with the product's title but feel free to change it if you wish to!
Keep in mind that by enabling this setting, doesn't necessarily mean that your annotation will always appear in the Gmail Promotion tab since Gmail is using a complicated algorithm to show annotations.