If email previews are just a tick box activity before you hit send on your campaigns, most tools will do the job. But, if you’re relying on them to offer real insight into how your product’s email flows will be received, and guiding improvements made to them, you deserve a tool you can rely on across the full scope of your emails, from signups to multi-factor authentication flows. Not least, because these are the flows that will have the biggest impact on customer experience should they go wrong.
We’re going to take a look at three of the ‘heavy hitters’ in the email preview space; Litmus, Email on Acid and Mailosaur.
| Mailosaur | Litmus | Email on Acid (basic) | Email on Acid (premium) | |
|---|---|---|---|---|
| Email client previews | ✅ | ✅ | ✅ | ✅ |
| Dark mode previews | ✅ | ✅ | ✅ | ✅ |
| Preview real, sent emails | ✅ | ✅ | ✅ | ✅ |
| Automated QA checks | ✅ | ✅ | ❌ | ✅ |
| Link validation | ✅ | ✅ | ❌ | ✅ |
| Image validation | ✅ | ✅ | ❌ | ✅ |
| Attachment validation | ✅ | ❌ | ❌ | ❌ |
| Automated email testing via API | ✅ | ❌ | ❌ | ❌ |
| CI/CD integration | ✅ | ❌ | ❌ | ❌ |
| Test environments with unique inboxes | ✅ | ❌ | ❌ | ❌ |
| Previews as part of end-to-end flow testing | ✅ | ❌ | ❌ | ❌ |
| SMS testing available | ✅ | ❌ | ❌ | ❌ |
| Engagement insights | ❌ | ✅ | ✅ | ✅ |
| Shareable previews (cross-team) | ✅ | ✅ | ✅ | ✅ |
| Project folders | ✅ | ✅ | ❌ | ❌ |
| Adjustable user permissions | ✅ | ✅ | ❌ | ✅ |
| Subaccounts | ✅ | ✅ | ❌ | ❌ |
| Enterprise SSO | ✅ | ✅ | ❌ | ❌ |
| Enterprise security controls | ✅ | ✅ | ❌ | ❌ |
| Dedicated account management | ✅ | ✅ | ❌ | ❌ |
Table 1- NOTE: comparisons within this table are based upon visible features of each product, as seen on their respective websites in February 2026.
With all of these options offering email client previews (including light and dark modes), the option to share previews with your team, and being ISO27001 certified and GDPR compliant, it can be tricky to know which tool is best suited to your team, so let’s break it down a little further.
Litmus
Litmus is primarily structured around email marketing campaign workflows. A platform combining client previews, pre-send quality checks, and engagement analytics in a single environment, it’s built for marketing teams managing scheduled campaigns with structured review/ approval processes.
Litmus is not positioned as a testing tool for application-level messaging. It does not publicly market functionality for automated email testing within CI/CD pipelines, hosted test inbox environments, or end-to-end user flow validation. This means that teams shipping product-driven messaging (e.g., password resets, order confirmations, onboarding flows) may find that Litmus is optimized more for campaign QA than runtime testing.
Pricing is provided via custom quotes, which requires engagement with their Sales team before full cost visibility is available, and this makes it feel less transparent for potential customers. Reviews also suggest that their recent acquisition by a parent company has resulted in a marked increase in pricing.
Email on Acid
Email on Acid is centred around marketing email campaign checks, with email previews sitting beside features such as email analytics and image validation. These options benefit marketers aiming to do basic checks of their campaign, e.g. how emails will look in certain inboxes, but will not benefit QAs aiming to conduct comprehensive email testing.
Further, while it supports manual testing and preview validation, Email on Acid is not positioned as a testing environment capable of generating previews as part of wider automated flows. Feature depth can vary considerably by plan tier, and many advanced validation capabilities are limited to higher-tier subscriptions.
Mailosaur
Mailosaur is a comprehensive email preview, email testing, and SMS testing tool. Designed for those in Marketing, QA, Engineers, and Product Management, it’s a one-stop-shop for those conducting end-to-end manual and automated testing on their transactional and promotional messaging, from basic link and attachment checks to OTP and magic link testing. With Mailosaur previews, you can see how your emails will look across countless devices, email clients, light and dark modes, and even both landscape and portrait orientations too.
Mailosaur is aimed at users who want to be sure that their email will be triggered, sent, arrive, and render as they intend, and those wanting to maintain customer trust during their most crucial messaging. To put it plainly, it’s centred around companies who care about the quality of their customer experience, and want to pre-emptively ensure their communications are of a high standard.
With a tiered pricing system and competitive pricing (which include optional add-ons), you can create a plan to suit you and contact the team to find out more about enterprise features such as SSO.
Why teams are moving to Mailosaur
Teams switching from Litmus or Email on Acid usually say the same things:
- “Our previews looked fine, but production emails still broke”
- “Personalisation wasn’t properly validated”
- “We had no way to automate testing”
- “SMS wasn’t covered at all, and we wanted a tool that could do everything”
- “Email QA lived outside our release pipeline”
Mailosaur fixes this by treating previews as one step in a complete messaging test workflow, not a standalone tool. Because of this, if your focus is on basic campaign QA and marketing workflows, Litmus and Email on Acid are strong, proven tools. Whereas, if your focus is transactional messaging quality across email and SMS, Mailosaur is purpose-built for the job.
If you'd like to give it a go, request a demo or start your 14-day free trial with Mailosaur any time.