How the Litmus Team Uses Email Guardian (and You Can Too!) - Litmus
Briefly

Every quarter, we test every single email template in our Litmus Design Library using Previews & QA to ensure there are no critical issues. Our focus here is to ensure that every single email and email template still displays (or renders) as expected in every email client and device.
Litmus Email Guardian helps us protect against unexpected changes that could affect our emails' performance.
Read at Litmus
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