How do you use these tools for QA in agencies?

Agency email QA is a layer cake: you're catching bugs before the client sees them, proving to the client you tested it, and protecting your own reputation when something goes wrong. Testing tools support all three, but the workflow matters as much as the tools.

The typical flow looks like this: design and build first, then test rendering across the client list of required environments. Most clients care about Gmail on mobile, Outlook on desktop (especially Outlook 2019, which has genuinely terrible CSS support), and Apple Mail. Test those first. Then check whatever else the client has asked for or that your data says their subscribers actually use.

Litmus and Email on Acid are the two tools most agencies use for rendering previews. Litmus also has spam filter testing and link checking built in. The agency workflow usually involves generating a preview in the tool, sharing the preview URL with the client for approval, and documenting that approval before sending.

A few practices that make agency QA more systematic. First, build a standard QA checklist that every campaign goes through, not just the complex ones. It's the simple campaigns that catch you out because no one double-checks them. Second, re-test after every change. If the client asks you to "just change the subject line," that's not a reason to skip testing. Third, document everything. Screenshot the approval. If a campaign has problems after send, you want to be able to show exactly what was approved and when.

For list validation before any client send, our free Review My Emails source analyzer can catch authentication gaps and formatting issues that affect deliverability. That's the kind of pre-send check that protects you from deliverability problems you'd otherwise only hear about after the fact.

If you're building or refining an agency QA process, email rendering testing covers what to check and why certain clients are harder than others.