We are certain that the Mobile vs. Desktop analysis that you can see with the Email Client & Mobile Device Tracking feature will make you want to test how your email newsletter is displaying on different devices and browsers. In case your subscribers open your emails from different email clients and seem to use their phones and tablets more and more each day for emailing, you would probably need to test your email in different email clients and see how it looks, and on different phones and tablets.
The most practical thing to do is to send your email newsletter to yourself, using all the possible combinations. We advise you to create your own accounts in yahoo, windows, google, aol, hotmail etc., then add those accounts into a mailing list you will create for testing purposes in your Moosend account. Then send your email campaign, and see how it displays in outlook, on phones (android and iphone), and on tablets inside your organization. Then of course you will need to test how it displays in Firefox, Internet Explorer, Safari, Opera, Google Chrome, as each of these programs picks up html in a different manner. Setting up a group of testing devices inside your organization to use every time before sending your campaign, will make it worth it.
The less images you put in your email newsletter, the better, as images are not always picked up. Many email providers never display images automatically, unless you ask them to. We understand that and exquisite HTML design may look beautiful, but the more image tags you have the less probabilities exist for them to appear correctly in the majority of systems. So try to be as minimalistic as possible with your email design, and you will not regret it.
Of course there are services you can use to preview your email newsletter before sending like previewmyemail or Litmus. Whatever it takes for your email to display correctly will make 20 minutes worth of testing.