Email on Acid

Key points

• Category: Design, templates & testing
• Pricing: Paid
• Best for: Teams that need client testing without a Litmus budget.
• Render and spam testing
• Accessibility review

What Email on Acid is

Email on Acid, now being rebranded by its parent Sinch as Mailgun Inspect, is a pre-send email testing and QA platform. Users submit HTML or send a test email and receive rendered screenshots across 100+ email clients and devices, similar in purpose to Litmus. It also runs automated checks including spam-filter content analysis, link and image validation, accessibility audits, and HTML code analysis. Sinch, which also owns Mailgun and Mailjet, acquired Email on Acid in 2021 and is folding it into a unified Mailgun-branded QA suite.

Teams use it primarily as a QA gate before campaigns go out: designers and marketers check rendering across tricky clients like Outlook's Word-based rendering engine and Gmail with images blocked, developers use the API to integrate testing into build pipelines, and some agencies embed it as a white-labeled tool inside their own platforms.

It sits in the design, templates & testing part of an email stack - build emails that render and read well everywhere. In practice it is the right pick when your priority is: teams that need client testing without a litmus budget.

What it does well

The capabilities teams rely on most are render and spam testing, accessibility review. Taken together these cover the day-to-day work in this category, and they are the features worth testing during a trial rather than reading about.

It is generally positioned as a lower-cost alternative to Litmus with comparably comprehensive rendering coverage (100+ clients) and solid built-in spam and accessibility testing, making it attractive to teams that find Litmus too expensive.

In real use the strongest points people report are good value; broad client coverage.

Key features

• Render and spam testing
• Accessibility review
• Good value
• Broad client coverage

Pricing tiers

Email on Acid is a paid product. Email on Acid/Mailgun Inspect is subscription-based with tiers around $74-99/month (Basic, limited previews and partial checks), roughly $134-199/month (Premium, adds spam testing and full content checks), a higher-volume Professional tier, and custom Enterprise pricing; overages are billed per additional preview.

Pricing pages move often, so confirm the current figures with the vendor before you budget. The number worth modelling is not the licence fee on its own but the cost per delivered email once bounces, suppressed contacts and spam-foldered sends are taken out.

Ideal customer profile

• Best fit: Teams that need client testing without a Litmus budget.
• Where it sits in the stack: Design, templates & testing - build emails that render and read well everywhere.
• Budget profile: Paid - suited to teams comfortable with this commercial model.
• Probably not for you if: interface feels dated in places would block your team.

What it connects to

Email on Acid is commonly wired into Mailgun, Mailjet, Postman (API testing), REST API for custom platform integration, White-label/embeddable API for SaaS and ESP platforms and Slack (via workflow tools). Check that the specific objects and events you rely on are covered, not just that a logo appears on the integrations page - shallow connectors are a frequent source of rework.

Where it falls short

No tool in this space is complete on its own. With Email on Acid the trade-offs to plan around are interface feels dated in places. None of these are reasons to avoid it - they are the gaps another layer of your stack needs to fill.

It is a testing-only tool with no email analytics or subscriber tracking of its own, its interface is considered less polished than Litmus, and its brand is currently being phased out in favor of Mailgun Inspect, which may cause transition friction for existing customers.

A useful test before committing: send a real campaign through your intended setup, then check where it actually lands across Gmail, Outlook, Yahoo and your customers' corporate filters. Tooling that looks identical on a feature list often behaves very differently once reputation and authentication are involved.

The essentials

Category

Design, templates & testing

Pricing model

Paid

Vendor

emailonacid.com

G2 rating

4.4 / 5

Best for

Teams that need client testing without a Litmus budget.

Works alongside Warmy

Yes - warm-up, placement, DMARC

Review scores are rounded public averages and change over time - treat them as indicative rather than exact.

How it fits a deliverability stack

Deliverability is decided by four things: the reputation of the sending domain and mailbox, the quality of the list, correct SPF, DKIM and DMARC authentication, and proof of where mail actually lands. Email on Acid covers part of that picture. The mistake most teams make is buying four separate products for those four jobs and still having no single place that tells them whether the last campaign reached the inbox.

Warmy runs warm-up, inbox placement testing, email verification and DMARC monitoring as one platform, which is why Email on Acid usually sits alongside it rather than against it: it keeps doing what it is good at, while reputation, placement and authentication are handled in one loop.

Its spam testing checks content against common filter rules and blacklist services, which helps catch obvious deliverability red flags before sending, but it does not provide ongoing sender reputation monitoring, seed-list inbox placement testing, or DNS authentication management - those require dedicated deliverability tools.