InboxEagle vs Email on Acid
Email on Acid is now Mailgun Inspect
Email on Acid was acquired by Sinch and rebranded as Mailgun Inspect. The emailonacid.com domain redirects to Mailgun. Core features remain the same under the new name.
These tools are compared together because both involve email deliverability — but they operate at completely different points in your workflow. Email on Acid checks what happens before you send. InboxEagle monitors what happens after. Understanding that distinction is the whole comparison.
Which one fits your situation?
Choose InboxEagle if…
- ✓Your campaigns are going to spam and you need to know exactly where and why — after real sends, not test submissions
- ✓You use Klaviyo or AWS SES and want placement monitoring without manual steps
- ✓You manage multiple client accounts as an agency and need per-client placement dashboards
- ✓You need domain reputation and complaint rate trends tracked continuously over time
Choose Email on Acid (Mailgun Inspect) if…
- →You need to verify rendering across 100+ email clients before every send
- →You want to catch broken links, oversized images, and HTML errors pre-send
- →Accessibility compliance (WCAG 2.2, ADA, EAA) is a requirement
- →You want pre-send spam filter content checks independent of sender reputation
InboxEagle: 14-day free trial · No credit card · Connects to Klaviyo in minutes
Start Free Trial →The Core Distinction
Pre-Send vs. Post-Send: The One Thing to Understand
Email on Acid — Before You Send
"Will this email render correctly and pass spam filters?"
You submit the email before sending. Email on Acid checks rendering across 100+ clients, validates links and images, analyzes HTML, and — on Premium — runs WCAG 2.2 accessibility checks and spam filter content tests.
What it can't tell you: where your campaigns actually land for real recipients, what your domain reputation is, or whether your complaint rate is trending toward Gmail's 0.10% filtering threshold.
InboxEagle — After You Send
"Where did this campaign actually land?"
InboxEagle connects to your ESP and records inbox, spam, and tab placement across Gmail, Outlook, Yahoo, and Apple Mail after every live campaign send — automatically, no manual submission required.
What it can't tell you: how your email renders on a specific device, whether you have a broken link, or whether your HTML is valid before you send.
Can You Use Both?
These tools don't compete — they cover different gaps
For eCommerce brands sending at volume, running both is the complete picture:
Email on Acid handles:
- —Will this email break in Outlook dark mode?
- —Is the unsubscribe link functional?
- —Does the HTML have rendering errors?
- —Will content-based spam filters flag this copy?
InboxEagle handles:
- —Did this campaign land in inbox or spam on Gmail?
- —Is my domain reputation degrading?
- —Which ISP started filtering my mail this week?
- —What are my competitors sending and where are they landing?
One prevents the problems you can see before sending. The other catches the problems that only surface in live delivery — and compound if left unmonitored.
Feature Comparison
Side-by-Side Features
| Feature | InboxEagle | Email on Acid (Mailgun Inspect) |
|---|---|---|
| Deliverability Monitoring | ||
| Post-send inbox placement monitoring | ✓ Automatic after every campaign | Pre-send seed testing only |
| Domain & sender reputation tracking | ✓ | ✗ No |
| Gmail / Outlook / Yahoo / Apple Mail | ✓ | Named in seed tests |
| IP reputation monitoring | ✓ | ✗ No |
| Integrations | ||
| Klaviyo integration (native) | ✓ Professional+ — campaigns, lists, metrics | ✗ No |
| AWS SES integration | ✓ Professional+ | ✗ No |
| Google Postmaster Tools | ✓ All plans | ✗ No |
| Intelligence | ||
| Competitor campaign monitoring | ✓ Professional+ | ✗ No |
| Post-campaign Deliverability Agent | ✓ Professional+ | ✗ No |
| Agency & Support | ||
| Multi-client agency dashboard | ✓ Agency plans (3–20 clients) | Unlimited users, no client workflow |
| Dedicated CSM | ✓ All plans | Phone/chat on Contract only |
| Pre-Send QA (Email on Acid only) | ||
| Email rendering previews (100+ clients) | ✗ No | ✓ All plans |
| Dark mode rendering preview | ✗ No | ✓ |
| HTML code analysis | ✗ No | ✓ Premium only ($199+) |
| Link & image validation | ✗ No | ✓ Premium only |
| Accessibility checks (WCAG 2.2) | ✗ No | ✓ Premium only |
| Pre-send spam content checks | ✗ No | ✓ Premium only |
| Trial | ||
| Free trial | 14-day, no credit card | 1 month free |
Highlighted rows = InboxEagle capabilities Email on Acid does not address. Red rows = Email on Acid capabilities InboxEagle does not address. These tools cover non-overlapping ground.
Pricing
Pricing Side by Side
InboxEagle
Post-send monitoring. Flat-rate. No per-test limits.
Starter
$249/mo
$209 annual
1 client · placement records · CSM
Professional Most Popular
$499/mo
$419 annual
+ Klaviyo · Deliverability Agent · competitor data
Enterprise
Custom
Full Agent suite · dedicated expert
Email on Acid (Mailgun Inspect)
Pre-send QA. Preview-based. $0.15 overage per preview.
Basic
$99/mo
1,000 previews/mo · rendering only · no spam checks
Premium
$199/mo
2,000 previews/mo · spam checks · accessibility · link validation
Contract
Custom
Custom volume · phone support
1-month free trial. Spam checks, accessibility, and link validation require Premium ($199/mo).
FAQ
Frequently Asked Questions
What is the difference between InboxEagle and Email on Acid?
Email on Acid (Mailgun Inspect) is a pre-send QA tool — rendering previews, HTML validation, accessibility, and spam content checks before you send.
InboxEagle is a post-send deliverability monitor — it records actual inbox placement after your campaigns go out, using automatic Klaviyo and AWS SES integrations. They address different problems and don't overlap.
Is Email on Acid the same as Mailgun Inspect?
Yes. Email on Acid was acquired by Sinch and rebranded as Mailgun Inspect. The emailonacid.com domain redirects to Mailgun. Core features remain the same.
Does Email on Acid monitor ongoing inbox placement?
Email on Acid includes an inbox placement seed test — but it's a pre-send manual check, not continuous post-send monitoring. It doesn't connect to your ESP to record placement after live sends.
InboxEagle does that automatically after every campaign through Klaviyo or AWS SES.
Can you use InboxEagle and Email on Acid together?
Yes — and for high-volume senders, using both is the complete workflow. Email on Acid catches pre-send issues: rendering errors, broken links, accessibility problems.
InboxEagle monitors post-send reality: inbox vs. spam placement, domain reputation trends, and campaign-over-campaign performance. No overlap, no redundancy.
Know what your email looks like. Know where it lands.
Email on Acid tells you how your email renders before you send. InboxEagle tells you where it actually lands after you send — inbox, spam, or promotions tab — automatically, across every campaign, with no manual steps.
Trusted by 2,000+ email senders · Gmail, Outlook, Yahoo, Apple Mail coverage