Litmus

Litmus is a comprehensive email testing and optimization platform used by marketers and email teams to ensure their emails look great and perform well across every client, device, and inbox. It’s widely regarded as an essential tool for QA and pre-send testing in professional email workflows.

With Litmus, users can preview emails across dozens of email clients (like Gmail, Outlook, Apple Mail, etc.), identify rendering issues, and validate that their campaigns are mobile-friendly and accessible. It also offers tools for spam testing, link validation, and image blocking scenarios.

Beyond testing, Litmus includes email analytics, collaboration features, and a builder for editing and reviewing HTML emails. Teams can streamline review cycles, leave feedback, and manage approvals directly within the platform, all while keeping version control intact.

Litmus is a critical addition to any email production stack, especially for teams that prioritize email quality, consistency, and deliverability. It integrates with major ESPs and helps marketers launch polished, high-performing campaigns with confidence.