Updated 30 October 2026. Originally published 17 April 2026. Pricing and product details checked on the update date.
An email can look right in your editor and still arrive with a broken layout, unreadable dark mode styling or a broken link. Email on Acid and Litmus help email and CRM teams catch these problems before sending.
Choose your QA tool around how you build and approve emails. Choose your analytics around the questions you need to answer after sending. Mailgun Inspect, Email on Acid’s successor, and Litmus help with the first part. SEINō gives your CRM team a dedicated place for email analytics, from engagement and revenue reporting to deeper analysis and performance monitoring. You can use it alongside your existing QA tools.
Litmus is now part of Validity Engage. This guide uses the familiar product names while comparing their current offerings.
Email on Acid vs Litmus at a glance
| Capability | Email on Acid / Mailgun Inspect | Litmus |
|---|---|---|
| Rendering previews | Previews across 100+ clients and devices | Previews across 100+ clients and devices |
| Technical QA | Premium adds accessibility, HTML, link, image and spam-content checks | Rendering previews and pre-send QA, with features depending on the plan |
| Review and approval | A testing step within your existing review process | Litmus Proof provides comments and approval workflows |
| Analytics | Pre-send QA is the focus of Inspect; the wider Mailgun suite includes other products | Subscriber engagement and reading-environment reports, aggregate reports and campaign comparisons |
| Ongoing monitoring | Separate from the analytics and technical monitoring available elsewhere in the Mailgun suite | Email Guardian monitors rendering, links, images and deliverability; package limits apply |
| Published pricing | Basic $99/month; Premium $199/month, with preview allowances and overages | Contact sales for a quote |
Product details: Mailgun Inspect pricing and features, Litmus testing, review and approval, analytics reporting and monitoring.
Our recommendation: shortlist Inspect when you need previews and technical checks within a production process that already works. Shortlist Litmus when building, reviewing and maintaining emails involves several people. For analytics, include SEINō when you want to connect email engagement to business results and keep track of the channel over time. Keep your pre-send checks whichever analytics platform you choose.
Check the email, then understand what it achieved
A successful QA check tells you the email is ready to send. Afterwards, your team still needs to understand who responded, what happened on the website and whether that activity led to purchases.
Litmus also covers post-send engagement analytics and technical monitoring. Adding SEINō gives you a dedicated analytics workspace for connecting those email results to the wider customer journey.
Email QA tools
1 · Before sending
Check the email
Will the experience work for the reader?
Analytics platform for CRM Marketing
3 · After sending
Understand the result
What happened across the customer journey?
What changed with Email on Acid and Litmus?
Email on Acid is becoming Mailgun Inspect. Subscription customers started transitioning in June 2026, with annual customers moving at the end of their current term. Existing previews and tests do not transfer, so check what you need to retain before migrating. Migration details.
Litmus is now part of Validity Engage. When buying today, use the current package details rather than the plan names in an older comparison. Validity Engage announcement.
Compare preview coverage with your own audience
Both tools cover more than 100 clients and devices. We would give more weight to the combinations your subscribers use than to the headline count: Outlook on Windows, a mobile Gmail app and Apple Mail in dark mode can present different testing requirements. Check the current Mailgun Inspect coverage and Litmus testing coverage.
Make a short list of the clients, devices and display modes that matter to your audience. During a trial, test the same finished email in both tools and inspect:
- Whether the main message and call to action are readable in light and dark mode.
- How the layout behaves on narrow screens and with longer content.
- Whether image alternatives and key information still make sense when images are unavailable.
- Whether links, tracking parameters and destination pages are correct.
- Whether each important dynamic-content variation has been included in testing.
Use the version produced by your actual sending platform. That lets you check the output after its templates, personalization and tracking have been applied.
Check the review workflow and integrations
Litmus Proof brings comments and approvals into the email review process. This matters when your designer, CRM marketer, brand team and client all need to sign off on the same email. Try it with those people, rather than judging the workflow from a demo alone. Litmus collaboration and review.
A good review process makes three things obvious: which version is current, what needs changing and who has approved it. Include everyone who needs access when you compare costs.
Your QA tool should fit the way you already create emails. You can use Mailgun Inspect with any email service provider. Litmus connects to a range of sending platforms and production tools. Look beyond an integration logo: can your team move the finished email into testing, make a correction and retest without awkward manual steps? Mailgun Inspect FAQ, Litmus integrations.
A useful trial task is to take one email from your editor through testing, revision and approval. Count the manual transfers and identify where feedback or versions become difficult to follow. An available API or integration is only helpful when it supports the steps you need.
Pricing: compare the testing volume you actually use
Mailgun Inspect starts at $99 per month. The more useful comparison for teams that need the additional QA checks is its $199 Premium plan:
| Mailgun Inspect plan | Published monthly price | Included previews | Users |
|---|---|---|---|
| Basic | $99 | 1,000 per month | Unlimited |
| Premium | $199 | 2,000 per month | Unlimited |
| Contract | Custom | Custom allowance | Unlimited |
Basic and Premium differ in more than preview volume. Basic includes rendering previews and API access. Premium adds accessibility tests, HTML code analysis, link and image validation, and spam-content checks. Include the tier that covers your required checks in your comparison.
Additional previews cost $0.15 on Basic and Premium. Each client or device screenshot counts separately, so one email test can consume many previews. Check current allowances when comparing costs. Plan details and preview definition.
For Litmus, request a quote. Ask for the preview allowance, review access, analytics and monitoring you need, plus any additional charges. That gives you a useful comparison with Inspect’s published prices.
Estimate repeat tests as well as campaign volume
Suppose your team checks 20 email versions each month across 30 client and device combinations, with three testing passes per version. That is 20 × 30 × 3 = 1,800 previews, assuming every pass tests every combination. This is an illustrative workload, not a vendor benchmark.
Include language versions, dynamic-content variations and retests after fixes in your estimate. Then compare the cost of that workload, along with review access and required features, under each proposal.
Run a small evaluation before committing
Choose a representative newsletter, a recurring lifecycle email and a message with dynamic content. Put the same emails through each tool, using the client coverage and reviewers your team needs.
Record whether the tool surfaces the problems you expected to find, how clearly it explains them, how easily you can retest and how the approval process works. Include the time spent moving between tools and chasing feedback.
Choose the tool that gets your actual emails through this process with fewer bottlenecks. A feature your team cannot use in its normal workflow adds little value.
Comparing email analytics? Include SEINō in your stack
The same team that checks an email before sending often needs to report on what it achieved afterwards. If you use Email on Acid or Litmus, you can keep those QA workflows and add SEINō as your dedicated email analytics platform.
Litmus already provides engagement analytics, aggregate reports, saved reports and comparisons across campaigns. These reports help you understand how subscribers read your emails and which email clients they use. Litmus analytics reporting.
We built SEINō to focus entirely on email analytics, with a data foundation your team can build on. We sync raw events from your connected platforms into SEINō, giving you the flexibility to organize the data around your campaigns, automations, audiences and brands. You can use that foundation to explore individual results and follow trends across your email channel:
- Connect engagement to business impact. Combine email results with website activity, conversions, orders and revenue from your connected sources.
- See trends over time. Follow engagement, conversion and revenue across weeks, months and years. Compare periods and customer groups to see whether a change is isolated or part of a wider pattern.
- Organize your data your way. Work from raw events and structure your reporting around the dimensions and groupings that matter to your team, with the flexibility to explore new questions as they arise.
- Build the views your team needs. Create dashboards and visual reports around your targets and reporting responsibilities.
- Keep track of performance. Use alerts and recurring insights to identify changes that deserve attention.
For example, a lifecycle email may render correctly while its revenue gradually declines. A QA check helps protect the email experience. In SEINō, you can follow that trend over time, break it down by audience and investigate whether engagement or website conversion changed. Litmus’s technical monitoring and SEINō’s performance monitoring address different questions.
If your QA process works, keep it. Add SEINō when you need richer reporting and a dedicated place to analyze and monitor your email channel. If analytics is part of your platform comparison, put us on that shortlist. The data you can analyze depends on your integrations and tracking, and attributed revenue should not be confused with proof of incremental sales.
Explore SEINō’s reporting and analysis or read our email marketing report guide for a practical reporting workflow.
Email on Acid vs Litmus: common questions
Is Email on Acid now Mailgun Inspect?
Yes. Mailgun Inspect succeeds Email on Acid. Migration timing depends on your subscription, and previous tests and previews do not transfer. Save what you need before moving. Migration information.
Is Litmus better than Email on Acid?
Litmus is worth shortlisting if collaboration, approvals and ongoing email monitoring are central to your workflow. Inspect is worth shortlisting if you mainly need previews and technical QA within your existing process. Test both with the same emails and people before choosing.
Does either tool guarantee inbox placement or accessible emails?
Automated checks help identify issues, but their results need review. A successful preview does not establish inbox placement, and an accessibility check is one part of assessing whether an email is usable. Include actual delivery data, representative test sends and human review in your QA process.
Can SEINō replace an email preview tool?
No. Keep a dedicated QA tool for rendering previews and checks before sending. SEINō focuses on email analytics and performance monitoring. You can add it alongside Email on Acid or Litmus to enrich reporting, or evaluate it when choosing the analytics part of your stack.