Gmail's few year back launched Promotions tab is a great example of email marketing. It not only help users sort promotions but also help in selecting and opting-out them easily with unsubscribe method. You can also learn through various designs from their emails display grid to make your own plan. In 2014 they introduced this grid view option in promotions tab which enabled users surf more confidently between various offers and visually appealing grids.
Promotions Grid view is not available by default in Gmail, for that you need to join "Field trial" which is a extra Gmail feature. Enable field trial.
Time frame plays crucial role while carrying out such promotions. If your promotions are time bound, you will likely get faster results. People do like offers, freebies, give away things, so use this method to attract your readers with additional tools such as new sign up requests for visitors, newsletters etc.
Additionally if you wish to add external HTML codes to have custom grid view to your emails promotion on websites, separate codes are available. Get it on litmus pages here.