Building responsive emails that render correctly on all the email clients is one of the biggest challenge for email developers now a days; even when the web technologies offer new features for building better websites fast, the majority of the email clients lack support for most of these features.
Additional that lack of support, the amount of email clients and their variations (device, web browser and version) is just too high. Fortunately for us – email developers – there are tools out there that allow us to test our emails in different clients, including their variations. Litmus is one of the most famed, offering the possibility to test emails easily, letting you choose which clients you want to target. 

Despite of being one of the most popular SaaS solution for email testing, litmus also offers a bunch of helpful tools for email developers, these are some of the most popular:

• Email Builder: HTML editor that offers syntax highlighting, live preview and integration for showing rendering in any email client.
• Checklist: Check content, links, tracking among other before scheduling a send. Subject line testing: Preview how your subject line will appear on different clients.
• Email Analytics: Get statistics on which email clients are used, engagement reports, geo location, etc.
• Litmus Scope: You like an email from your inbox? Visualize it in both mobile and desktop, extract it’s code and play around with it.