2 sites where you can test the display of emails before sending
Emails appear differently in each email client because each client has its own rules for display, and not always supports html styles.
Gmail or Outlook? iPhone or Android? We need to see a preview of our email before sending, and for this reason there are today two sites online that allow you to do. They allow you to preview in 45 different email clients and mobile devices in just a few minutes. These tools also offer other services such as spam tests, analysis of the email, html code optimization, etc.
Litmus
From $ 79 a month

Litmus allows almost instant preview of our email, just by sending an email to a mailbox that is provided by them or by copying and pasting text into a separate html text area.It offers a free profile that allows you to test service for outlook, gmail and iPhone 6.
Email on acid
From $ 45 a month

As well as the previous one, it allows you to test the display of e-mail for more than 60 email clients simultaneously. Unlike Litmus, you can buy credits to test your email without any subscription.