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What is Email on Acid and What are the Alternatives?

Let’s cut right to the chase, shall we? If you want an Email on Acid alternative, you’re here for one of two reasons:

  1. You’re searching for email testing tools and want to compare your options.
  2. You’re unsatisfied with Email on Acid for some reason, and you need an alternative.

You probably realize you’re visiting the Email on Acid blog right now. And you may assume we’ll be biased... that you won’t get an honest comparison of similar tools. That’s understandable.

If you’re in the first group, we promise to do our best to give you a straightforward explanation of these different platforms and services. If you’re in the second group, the least you can do is hear us out before you cancel. Right?

What is Email on Acid?

Before we explore the alternatives, it might help you to know exactly what Sinch Email on Acid does and why you’d want to use (or keep) it in the first place.

We built this platform to help senders with email quality assurance (QA). For most businesses, the email channel is very important for communication, marketing, and the overall customer experience. Senders need each message and every campaign to look its best and function as expected after arriving in subscribers’ inboxes.

However, achieving email perfection is much easier said than done. One of the biggest challenges is that different email clients have varied levels of support for HTML and CSS. They also use their own email rendering engines, which means the way a campaign looks in Gmail or Yahoo Mail could be very different in Outlook or Apple Mail.

Testing mobile email clients

What are email previews?

A key feature of our platform is the Email Preview engine, which shows you how an HTML email campaign renders on more than 100 clients, live devices, and mobile operating systems. This form of email testing happens before you hit send so you can troubleshoot and fix problems instead of finding out later that you sent a broken email to thousands of people.

Our email previews are screenshots that show users exactly how their campaigns are rendered in different scenarios. It could be Apple Mail on an iPhone 13 in dark mode or on a Pixel 5 in Gmail running Android 13 (just to name a couple). You send a test email, and we send you back a collection of screenshots for review. Check out this sample test result to see it for yourself.

This may sound simple and straightforward. But keeping things running isn’t as easy as you think – just ask our product team and software engineers. That’s why there really aren’t many comparable Email on Acid alternatives out there.

Some teams conduct manual email marketing QA, which means they send test emails to colleagues for review. While that’s better than nothing, it still leaves a lot of room for inaccuracy and human error.

Email on Acid features and benefits

You could also describe Email on Acid as an automated email marketing checklist. That’s because the benefits go beyond previews. If you’re currently using our software for previews only, there may be some tools you can start taking advantage of.

What else can Email on Acid do?

  1. Inbox Display: Optimize your subject lines, preview text, and sender name to improve open rates and ensure visibility on mobile devices.
  2. Accessibility checks: Add image alt text, check color contrast, and optimize your email for screen readers. This ensures every subscriber can easily engage with what you send.
  3. Deliverability checks: Check your IP address against major blocklists and spam filters before you hit send. This helps you avoid inbox placement issues that drastically reduce email ROI.
  4. Link Validation: Check every link in your email to be sure you never send subscribers to a 404. Replace broken links in real time. Plus, add missing UTM parameters for tracking visits to your website.
  5. Image Validation: Optimize images and graphics for the email inbox. This feature helps improve load time and lets you modify animated GIFs for Outlook.
  6. Spell Check: Make a final check for any typos and spelling errors before your campaign launches. This feature includes a profanity filter to help protect your brand reputation. We’ll check alt text and preview text for mistakes too.
  7. Edit email code: When you notice a rendering issue in an email preview, you don’t have to leave the platform to fix it. Troubleshoot and adjust code without going back and forth between your ESP and testing platform.
  8. Email Analytics: Go beyond the basic email metrics to gain a deeper understanding of your contact list. Our advanced analytics feature insightful engagement data such as Read, Glance, Delete rates. Plus, see geolocations, get heatmaps, and find out which clients your subscribers are using to view your emails. You can even filter out prefetch opens to improve the accuracy of reporting.
  9. Collaboration: Team management features let stakeholders review, comment, and approve campaigns during the QA process. You can also customize user roles and permissions to control access.

Perhaps the biggest benefit of using Email on Acid is that we offer unlimited testing with every paid plan. That means you can test as much as needed and see as many email previews as you want. Unlimited testing is a valuable differentiator you won’t find with many of our alternatives.

Why finding an Email on Acid alternative is confusing

Question mark on options for email testing alternatives

If you research email testing alternatives on some of the popular software review and comparison sites, you might get a little mixed up. That’s because there are different types of email testing with specific purposes.

Not all these services mentioned on tech review websites offer email previews. In fact, most do not. Some are for email validation testing. Others are for email A/B testing, and still others may be for SMTP testing and spam testing.

Even reputable websites like Gartner as well as G2 seem to be missing the mark when comparing Email on Acid alternatives. You’ll find completely unrelated SaaS brands listed as potential options, including CRMs like Salesforce. That’s just plain confusing and inaccurate.

What Email on Acid is not

To help you figure out what you really need and decide whether you’re ready for Email on Acid or another option, here are a few things our platform does not do:

  • Email on Acid is not an email service provider (ESP). That means you don’t use it to send emails or manage your contact lists.
  • Email on Acid does not offer a WYSIWYG email builder. While there is an Email Editor in our platform that lets you code campaigns from scratch, it’s generally used for find-and-fix functionality. There is no drag-and-drop email editor for non-coders.
  • Email on Acid is not for address validation. Verifying email contacts and conducting list hygiene is not part of our current offering.
  • Email on Acid is not marketing automation. Even though we talk about “workflows” for email QA and help automate the process, our software is not used to build automated email workflows.
  • Email on Acid is not a complete deliverability solution. While we do offers spam testing and pre-send checks to ensure you’re not on a blocklist, there are other options that provide more comprehensive support for improved inbox placement.
  • Email on Acid does not test SMTP or automated email sequences. We streamline QA for email marketers rather than for software engineers who are integrating email into apps and testing email infrastructure.

10 Email on Acid alternatives: Pros and Cons

This list of options focuses only on software that provides similar services to Email on Acid. It’s also possible that you will find ESPs and CRMs that offer email client previews. In many cases, these providers are using an API to white label the feature. The previews in these platforms often come from Sinch Email on Acid or our top competitor.

1. Litmus

Litmus logo

Litmus is the other recognizable name in email pre-deployment testing. When you come across online discussions about testing HTML emails, both brands are often mentioned together.

Interestingly, there are some email marketing teams who choose to use both Email on Acid and Litmus. That tells you something about how important this process is.

While there are differences between our two platforms, their main purpose is similar. Litmus offers more advanced features like a way to centralize brand assets, a drag-and-drop visual editor, and email personalization tools.

Litmus is certainly the most expensive Email on Acid alternative. You’ll need to decide if the extras that come with Litmus are helpful. If you already have tools to design and personalize email campaigns, you may not want to pay for what you don’t need.

You’re probably smart enough not to fall for those product comparison pages that inaccurately spin things to make one brand look perfect and the other look horrible. But just in case you want to see them:

Litmus - Pros

Like Email on Acid, Litmus provides comprehensive email client previews. Although, our screenshots do sometimes deliver different results for the same clients and devices.

Litmus can also be used as a tool to build email campaigns. However, you’ll still need an ESP to send emails. And that platform you’re using may already have a sufficient email building solution.

The personalization features from Litmus could be a valuable way to increase email engagement, assuming you don’t already have an adequate solution for personalization.

Litmus – Cons

Besides a higher price tag, the biggest downside of Litmus is that you will not enjoy the benefit of unlimited testing. Paid plans from Litmus have a set number of monthly email previews. When you exceed the volume limit, you are charged for overages.

Here’s what a Reddit user had to say about receiving overages from Litmus:

“I just got notice that my usage of email previews far exceeds what the basic account structure allocates -- which was news to me that it even counted it that way!

I'm pinging you all here to get a better understanding of the best way to use Litmus as it is marketed, without incurring--quite frankly--insane overcharges.”

You don’t have to worry about that with Email on Acid (just sayin’).

2. Mailgun Optimize

Sinch Mailgun logo

Mailgun Optimize is a comprehensive deliverability suite. It includes email previews that are powered by Email on Acid’s technology.

Pairing email deliverability with email previews makes a lot of sense. The way an email renders is part of deliverability. Rendering is a bit like the grand finale of inbox placement. For example, if an important campaign reaches the inbox, but it’s unreadable on a popular email client like Outlook, it may as well land in spam. That’s because your subscribers won’t be able to engage with it. So, what’s the point?

While previews are an excellent feature of Mailgun Optimize, the platform excels at providing insights to improve inbox placement. That includes sender reputation monitoring, solutions for email validation, and inbox placement reports. Users can integrate with services like Google Postmaster Tools as well as Microsoft SNDS.

Mailgun Optimize - Pros

You don’t have to use Mailgun as your ESP to take advantage of Mailgun Optimize. So, if you are looking for a deliverability solution as well as email previews, this is a convenient option.

If you’re concerned about the 2024 sender requirements from Gmail and Yahoo Mail, this tool can even help you check to make sure email authentication protocols are working correctly while keeping tabs on your sender reputation with Gmail.

Mailgun Optimize - Cons

Like Litmus, Mailgun Optimize has limits to the number of monthly previews available to users. Unlike Litmus, Mailgun is much more transparent about overages – listing them on the pricing page.

While Mailgun Optimize has more robust deliverability tools than Email on Acid, it doesn’t provide the same solutions for email QA that are available within our automated Campaign Precheck workflow.

3. Everest from Validity

Everest logo on blue mountain background

Everest from Validity bills itself as an “email success platform” that focuses on deliverability and increased engagement. It includes some features that are similar to Mailgun Optimize. It does not, however, offer as much in the way of email client previews.

Once upon a time, Everest was known as the separate services ReturnPath and 250ok, which used Email on Acid’s preview engine. Then there was this whole lawsuit thing that we’re not at liberty to discuss on our blog.

Today, what Everest offers are Design Tests. The site suggests that this is more for seeing how your email campaigns are displayed on different screen sizes (desktop, smartphone, tablet).

Everest - Pros

An interesting aspect of the Everest platform is its Competitive Intelligence feature, which could help senders differentiate themselves in terms of things such as subject lines and send times.

It’s designed to support email performance through deliverability and engagement improvements, but it’s lacking in terms of previews for pre-send email testing.

Everest - Cons

Everest is much more limited when it comes to the breadth and depth of previews available for testing. It states it offers nearly 20 email client previews (or 70+ email applications) whereas Email on Acid and Litmus provide more than 100.Design tests from Everest are also limited based on the plan. You’ll get zero of these email tests at the lowest pricing tier.

4. Email Preview Services

Email Preview Services (EPS) is a SaaS company based in Ukraine. As the name suggests, previews are the main feature of this service.

EPS also has spam testing, provides some analytics, and has an HTML email editor for building or fixing campaigns.

Like Email on Acid and Litmus, this alternative sends its users screenshots from inside live inboxes to review for problems. However, the breadth and depth of clients and device previews available is considerably less than the leading options.

Email Preview Services - Pros

Like Email on Acid, EPS customers get unlimited email previews each month. If previews are all you need, this also provides a cheaper, yet less-comprehensive alternative. The site currently only lists around 50 clients. Missing, for example, are previews from devices running the latest Android operating system. As of this writing it’s also missing previews for the latest iPhones.

Because new versions of smartphones are popular with consumers, and mobile carriers push people toward regularly updating their phones, you’ll want to be sure you’re getting previews from the latest devices.

Email Preview Services – Cons

While checking out previews may be a crucial step in the email QA process, it usually comes at the very end – once all the other possible problems are addressed. What EPS users are missing is a full quality assurance solution for email marketing.

There are no accessibility checks, no inbox display previews for subject lines, no image or URL validation for graphics and links. It’s also missing collaboration features, which allow teams to comment and approve screenshots before a campaign launches.

5. Mailosaur

Mailosaur logo

Mailosaur is software for testing both email and SMS. The platform’s most robust capabilities involve testing automated email and SMS workflows.

While it does offer some solutions for marketers, its strength may be in serving software engineers and those who are programming applications. Mailosuaur provides features like a developer sandbox and integrations with other testing platforms, including Cypress, Playwright, and Selenium.

While Mailosaur talks up its email previews, it turns out this feature is only available as a “bolt-on,” which we think is a cool way of saying you have to pay extra for it.

Mailosaur – Pros

If you need a solution that provides email and SMS automated workflow testing, Mailosaur looks like a valid option. As an Email on Acid alternative, however, it’s not quite comparable. The platforms seem to serve different primary audiences, and email previews are not a core part of the Mailosaur product. It does provide other key pre-send testing features such as checking for broken links.

Mailosaur – Cons

As mentioned, email client previews are only available as an add-on to the Mailosaur product. There’s no clear information on the website about what those additional costs are. While it may be ideal for email automation QA, it lacks some important features for email marketing QA.


Parcel logo

Parcel is an email design and development tool that’s become very popular with email geeks who write code. Our own Megan Boshuyzen uses Parcel to code campaigns and run a component-based email design system.

Users can see live previews of different screen sizes while they’re coding. They can also send test emails to get screenshots sent back from a wide selection of clients and devices. Parcel provides email previews on more than 80 clients and devices

Parcel – Pros

If you want to test and preview HTML email campaigns as you code them, Parcel makes that very convenient. It’s a great tool for email developers because it also allows you to build a library of reuseable components.

For the non-coders on your team, there’s also a visual editor and team management features for collaboration.

Parcel – Cons

Parcel’s Inbox Previews are an add-on to the platform that starts at $49 for 500 previews per month and provides a pay-as-you-go model for additional previews.

7. Mailtrap HTML Checker

mailtrap logo

Mailtrap is a similar solution to Mailosaur in that it claims to help dev teams test, send, and control email infrastructure from one place. Beyond that, the platform also offers an HTML email checker that looks for code compatibility among popular email clients.

In this Mailtrap blog post covering different email preview tools, the writer even lists the product as better for software engineers than marketers, separating Email on Acid and Litmus into the marketing tool category.

Mailtrap – Pros

The previews in Mailtrap’s solutions are an acceptable alternative for software engineers who need previews along with other types of email testing and QA for sending. It claims to provide the most email clients on the market, but does not provide a definitive number. Mailtrap may be a good way for email marketers and software engineers who are developing automated workflows to connect and collaborate.

Mailtrap – Cons

As they point out, while it does provide previews, Mailtrap isn’t necessarily a tool for email marketing teams. If your goal is to optimize newsletters and promotional email campaigns for different inboxes, you may end up with a more technical tool that is missing helpful features for marketers.

8. HTML Email Check

HTML email check logo

HTML Email Check is a platform that primarily keeps email developers in mind. The offerings are separated into validation features and utility tools. Validation services include things such as HTML and CSS validation as well as link and image validation.  It also lists features to validate accessibility and mobile responsiveness.

To be clear, this software does not include email validations, which verify the legitimacy of email contact data for improved list hygiene.

The utility tools include checks for dark mode and an HTML editor among others.

HTML Email Check – Pros

This is a tool that specifically targets people coding HTML emails, which is nice. It’s built to help email developers find and fix problems with their code based on known best practices, email client support, and potential issues. But it’s missing a key component that helps email developers overcome email client rendering inconsistencies.

HTML Email Check – Cons

If you’re looking for a service that delivers actual screenshot previews from the most popular email clients and devices, you won’t get that from HTML Email Check.

The Visual Editor and Visual Editor Inspector tools explicitly state they are for “non-client specific devices”. Take that to mean you’ll see how an email will appear on desktops, tablets, and mobile phones (screen sizes), but not from inside actual email inboxes.

Also, if you need a collaborative solution for an email marketing team, this tool is mainly useful to coders.

9. Inbox Pirates

Inbox Pirates logo

Inbox Pirates is a Chrome extension that aims to provide preview services with a click. What’s not so clear is how well it works for previews of HTML email campaigns. The demo on the site only shows someone using a plain text email sent from a Gmail account.

Inbox Pirates does say that it integrates with a few popular platforms like Mailchimp and Hubspot as well as SendinBlue and The focus also seems to be on inbox display previews rather than how an HTML email looks once it is opened.

Inbox Pirates – Pros

Inbox Pirates previews include how a message appears in the notification bar/lockscreen of mobile phones. That’s an interesting feature since it’s often the first place a contact sees your subject line and preview text.

Based on the demo, the tool seems to be designed mainly for sales teams looking to preview cold emails.

Inbox Pirates – Cons

Inbox Pirates says it provides previews from 20+ email clients, which is far less than most other alternatives. According to the Chrome web store, as of this writing, the Inbox Pirates extension was last updated in October of 2022. New devices have been released since then.

Inbox Pirates does not provide unlimited previews. Its pricing structure is confusing. The Basic plan, for example, limits users to 4 previews/day or 10 previews/month. That makes it sound like you’d hit your limit in less than three days.

10. Testi@

Testi@ is another service that's purely dedicated to email rendering previews. Like InboxPirates, it also offers a Chrome extension. The site indicates it has the ability to generate screenshots from more than 100 rendering scenarios on different clients, devices, and operating systems.

Testi@ offers a free version, but that includes previews for just two webmail clients. According to its FAQ page, they are Gmail and Yahoo Mail on a Chrome browser. In addition to the screenshots, you can also use Testi@ to send test emails to up to 15 addresses for manual review.

Testi@ - Pros

This is a cheaper alternative that offers a pay-as-you-go model instead of a subscription. Rather than auto-renewing, you can choose the number of users and months you want to use the service. This might be a good option for senders who choose to test their email templates occasionally rather than testing every campaign before they send. But there are risks that come with not testing every email every time. You'll notice the price doubles with every month or user you add.

Testi@ - Cons

If email previews are all you want, this could work. But you'll be missing many of the additional checks that can add value and help optimize emails for performance and deliverability. More advanced services will offer advice on how to fix issues with email code, and some will even make automatic adjustments. Testi@ is limited to generating previews.

Testi won't tell you if your emails are meeting accessibility standards, for example. You also can't use it to check your links (unless you do it manually), spell check email copy, or preview inbox display.

Free Email on Acid alternatives

There’s no such thing as a free lunch. There are some free email testing and preview tools available, but you’re basically going to get what you pay for.

PutsMail: This a free tool for manual email testing that Litmus acquired in 2014. PutsMail makes it easier to send test emails to up to 10 inboxes for review. You paste in email code and enter email addresses for sending tests. Access to actual previews/screenshots is locked, and you will be pressured to sign up for Litmus.

MailNinja: For the price of your contact info, MailNinja will send you a link to its free email preview tool. It lets you paste in code to see how it looks on mobile and desktop as well as with images on or off. It does not show you email previews from specific clients and devices or alert you about any problems to fix.

Keep in mind, many of the subscription and pay-as-you-go options above also offer a free version or free trials of the email testing platforms.

Got more questions? We can help.

There’s a lot to digest here, we know. If you have questions about how Email on Acid works or anything else related to our platform, don’t hesitate to send a message and contact us.

You can also request a custom demo to find out more about how your organization can take advantage of Email on Acid. If you’d rather check things out for yourself, take advantage of our 7-day free trial and give our tools a test drive.

If you’re a current user who’s feeling frustrated, we welcome your feedback and we’re here to help. Please get in touch with customer support. Live chat will likely get you the fastest response. You can also post questions or concerns about our product in our vendor channel on the Email Geeks Slack.

Simplify the Email QA Process and Deliver Perfection

What’s the best way to run through your pre-send checklist? With Sinch Email on Acid’s Campaign Precheck, we’ve simplified the process and set everything up for you. Use it to double-check your content, optimize for deliverability, ensure accessibility, and preview how campaigns look on more than 100 of the most popular clients and devices. All before you hit send!

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