Litmus is an email testing and analytics tool, helping get round the problems of compatibility in email marketing. With Litmus, you can check how your email marketing messages render for different users across various devices and email clients, giving you the ability to test email on scale and identify problems at a glance. This is great for getting round email formatting differences, so you can tweak your email to present correctly, whoever the recipient. The spam test is really useful in ensuring stronger delivery rates, while the analytics function goes much more in-depth than other email marketing tools.