Email on Acid: What It Actually Does, What It Costs, and Who It Fits
A budget-friendly email preview and QA tool covering the same core rendering and spam-testing ground as Litmus, now being rebuilt by Sinch under the Mailgun Inspect name.
Email on Acid covers the same core ground as Litmus, rendering previews across 100+ email clients and devices plus spam and accessibility checks, at a noticeably lower starting price of roughly $99/month. It is being folded into Sinch's rebuilt Mailgun Inspect platform through 2026, with existing customers migrating at contract renewal and the core testing features carried forward. It is the pragmatic pick for teams that want reliable pre-send QA without paying for Litmus's deeper analytics tier.
What Email on Acid Is For
Email testing (or email QA) tools let a team preview exactly how an email will render before it goes out, across the many inbox providers, devices, and light and dark mode combinations a real subscriber list actually uses, so a broken layout in Outlook or a clipped subject line on a phone gets caught before it reaches a full list rather than after. Most also run a spam-filter check and an accessibility check alongside the visual preview, since a technically correct email that lands in spam or is unreadable to a subscriber using assistive technology fails just as badly as one that renders wrong.
Email on Acid built its reputation as a lower-cost alternative to Litmus with a comparable core feature set: rendering previews across 100+ email clients and devices, spam content checks, and HTML and accessibility validation. It is now owned by Sinch, the parent company of Mailgun, and is being rebuilt on Mailgun's infrastructure under a new name, Mailgun Inspect, with the migration rolling out through 2026 and existing Email on Acid customers moving over at contract renewal. For teams comparing tools today, it remains a pragmatic pick for solid pre-send QA at a noticeably lower price than Litmus, now with Sinch's backing investing further in the product.
Key Features
- Rendering previews across 100+ email clients and devices, comparable core coverage to pricier competitors
- Spam content checks on mid and upper plans that flag likely spam triggers before you send
- HTML code and accessibility validation that catches broken markup and readability issues
- Link and image validation to catch broken links and images before send
- Being rebuilt into an expanded QA suite, Mailgun Inspect, under Sinch, with added accessibility and spam analysis
Pros & Cons
Pros
- ✔ Comparable core email-preview and spam-testing coverage to Litmus at roughly a fifth of the entry-tier price
- ✔ A free trial available on entry plans without needing a sales call to get started
- ✔ Now backed by Sinch's Mailgun infrastructure, bringing more investment behind what was previously a smaller standalone company
Cons
- ✕ Currently mid-transition into the Mailgun Inspect brand, so plan names, documentation, and support may shift through 2026
- ✕ Analytics and personalization depth generally do not match Litmus's more mature post-send tracking
- ✕ Higher usage, more monthly previews or seats, still pushes cost up quickly through per-preview overage charges
Pricing
| Tier | Price (approx, billed monthly) | What you get |
|---|---|---|
| Basic (Mailgun Inspect) | Roughly $99/month | About 1,000 email previews a month, 100+ client and device rendering, accessibility and HTML checks, and link and image validation |
| Premium (Mailgun Inspect) | Roughly $199/month | About 2,000 email previews a month, plus built-in spam content checks and expanded QA tooling |
| Enterprise | Custom, quote-based | Custom preview volume and team size, negotiated directly with Sinch and Mailgun sales |
Sinch is migrating Email on Acid subscribers to its rebuilt Mailgun Inspect platform through 2026; annual-plan customers move over at renewal, with core testing features carried forward under the new name.
Pricing checked as of mid-2026 and hedged as approximate - Email on Acid is actively transitioning into Sinch's Mailgun Inspect platform, so plan names and rates may change during the migration; confirm current figures directly on Mailgun's pricing page before budgeting.
Common questions
Yes. Sinch, which owns Mailgun, acquired Email on Acid and is rebuilding it as Mailgun Inspect, with existing subscribers migrating through 2026 (annual-plan customers move over at renewal). Core email-preview and QA features are carried forward under the new name.
Not an ongoing free tier for its main preview product, but it offers a free trial on entry plans, and its starting price of roughly $99/month for the Basic plan sits well under Litmus's entry pricing.
For the core job, rendering previews across 100+ email clients and devices plus spam and accessibility checks, it is broadly comparable. Litmus still leads on post-send analytics depth and overall breadth, but Email on Acid, transitioning to Mailgun Inspect, is generally the more affordable route to the same core QA workflow.
Sinch, the parent company of Mailgun, owns Email on Acid and is folding it into Mailgun Inspect, its rebuilt email QA suite.
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