Here’s the short answer: Every email client, such as Gmail or Outlook, reads HTML differently.
Every time you send out an email it is coded in the magical language of HTML. It doesn’t matter if you created it in the Basic Editor or the Advanced Editor or if you ever looked at the code. HTML is the language of email and the web and it lies beneath the surface of every email.
Now, every email client (think Gmail, Hotmail, or Outlook) has developed their own way of reading the HTML. Think of it like a differences in the English language. We spell color and our British friends spell colour. I say soda and my friends in the South say Coke. Neither interpretation is right or wrong, just different. Same goes for our email client friends.
So, why does it matter? Generally the differences between email clients are small and hard to detect. HOWEVER, occasionally the differences are quite noticeable and drastically change the look of your email. Sometimes one client might even break your email completely.
Enter the fun of email testing. It can be tempting to just send away once your email is completed, but without testing in the major email clients you are at risk of a major email faux pas. We recommend that you test your emails on the major email clients such as Gmail, Hotmail, Yahoo, and Outlook. It is also important to test your email on mobile devices such as iPhones.
If you want to take the time and headache out of testing, check out Bright Peak’s email analysis service. They will test the email in all of the major email clients and mobile devices and give you a screen shot of the results to check for discrepancies.