Across multiple CRM audits we have run for consumer apps, the same pattern keeps appearing: email open rates look healthy at 18-25%, click-through rates hover around 2-4%, but actual in-app actions from those clicks sit below 0.5%. That is a 90%+ drop-off between the inbox click and the intended app action.

The culprit is rarely the email copy. It is the journey after the click. A user taps "View Your Rewards," lands on a mobile browser page, gets redirected to the app store, opens the app to the home screen, and has no idea where those rewards are. For lifecycle and CRM teams, this is not a minor UX issue. It is a measurement and revenue problem. Deep linking solves this, but email introduces unique technical challenges that standard implementations do not account for.

The Email-to-App Friction Problem

The friction between email and app is structural, not cosmetic. Unlike paid ad clicks that happen inside Meta or Google's controlled environments, email clicks pass through multiple intermediary layers before reaching the device.

Here is what typically happens when a user taps a link in an email: the ESP wraps the link in a tracking redirect, the redirect fires and logs the click, it resolves to your intended URL, then the device decides whether to open the app or the browser, and finally (if the app opens) the user may or may not land on the correct screen.

Each step introduces latency and potential failure. ESP redirect chains can break Universal Links on iOS entirely, because Apple requires a direct tap on a registered domain to trigger app opening. When an intermediary domain sits between the tap and your app's associated domain, iOS falls back to the browser. Even users who have your app installed get dumped into a mobile web page. From there, they either abandon or start a disconnected session your attribution cannot tie back to the email.

This is why deep linking that preserves context through every redirect matters more for email than for any other channel.

How Deep Links Work in Email

Standard deep links (URI schemes like myapp://screen/rewards) do not work reliably in email. Most email clients strip custom URI schemes entirely for security reasons. Gmail, Outlook, and Apple Mail all handle links differently, and ESPs add their own redirect layers on top.

The reliable approach uses HTTPS-based deep linking via Universal Links (iOS) and App Links (Android). These use standard https:// URLs associated with your app through configuration files on your domain (apple-app-site-association for iOS, assetlinks.json for Android).

The flow: your ESP wraps the link in a click-tracking redirect, the user taps in their email client, the redirect resolves to your deep link URL (e.g., https://yourapp.link/rewards?user=abc), the OS checks whether this domain is registered for app opening, and if the app is installed, it opens directly to the rewards screen with the parameters preserved. If not installed, deferred deep linking stores the context and routes through the app store.

The critical technical challenge is step 3. Most ESPs use their own tracking domains for click wrapping, which means the domain the OS sees after the tap is the ESP's domain, not yours. Since your app is associated with your domain (not the ESP's), the Universal Link handoff fails.

Three approaches to solve this:

ESP link wrapping bypass. Some ESPs (like Braze, MoEngage, and CleverTap) support custom tracking domains or direct link passthrough that preserves Universal Link behaviour. This is the cleanest solution when available.

Link page intermediary. Route the ESP redirect to a lightweight web page on your registered domain that detects the device, checks for the app, and either triggers the app open or redirects to the store.

Deep link with fallback. Use your dynamic deep link as the destination URL inside the ESP, configured to handle both app-installed and app-not-installed scenarios with a web fallback bridge page.

Handling Gmail, Outlook, and In-App Browser Edge Cases

Email clients are not browsers. They render HTML differently, handle links differently, and introduce their own intermediary layers. Here are the edge cases that break deep links most often.

Gmail on iOS. Gmail opens links in its own in-app browser (not Safari). Since Universal Links require a tap from Safari or the OS-level link handler, links opened inside Gmail's in-app browser will not trigger app opening. The workaround: your landing page must include an explicit "Open in App" button that uses a Universal Link, or implement a smart banner that prompts the user to switch to Safari.

Gmail on Android. Gmail on Android handles App Links more reliably, but only if your assetlinks.json is properly configured and the app has been set as the default handler. If not, Android shows a disambiguation dialog.

Outlook. Outlook on both iOS and Android uses its own in-app browser, similar to Gmail. Universal Links often fail to trigger, and Outlook's in-app browser has aggressive caching that can serve stale landing pages.

Apple Mail. The best-case scenario. Apple Mail respects Universal Links natively, so taps on properly configured links will open the app directly. This works for both the native Mail app and the default Mail configuration in iOS.

Practical workaround for in-app browsers. Since Gmail and Outlook dominate mobile email opens, your deep link landing page needs to detect in-app browsers and show a clear "Open in App" interstitial. This page should load fast (under 1 second) and display the value proposition from the email so the user does not feel lost.

Design your email deep links assuming the worst case (in-app browser, no Universal Link support) and let direct app opening be a bonus.

Deferred Deep Links for Lapsed Users Who Uninstalled

CRM campaigns do not just target active users. Re-engagement emails go to dormant and churned users, and a meaningful percentage will have uninstalled the app. Without deferred deep linking, these users tap the email link, land on a web page, and the campaign's re-engagement intent is lost.

Deferred deep linking preserves link context (destination screen, parameters, campaign data) through app store installation. When the user installs and opens the app, the deferred deep link routes them to the exact screen the email promised.

This matters for three reasons in CRM campaigns:

Re-engagement completion. If your email says "Your ₹500 cashback expires in 48 hours," the user who reinstalls needs to land on the cashback screen, not the onboarding flow. Without deferred deep linking, the reinstalled user starts fresh with zero context.

Attribution accuracy. Deferred deep links carry attribution parameters through the install. Your CRM platform can track the full journey: email sent, opened, link clicked, app reinstalled, cashback redeemed. Without this, the reinstall gets attributed to organic, and your email campaign shows zero reinstalls.

Personalisation continuity. Deferred deep link parameters can carry user identifiers, offer codes, or segment flags that restore the user's context immediately after install.

The implementation requirement: your deep linking provider must support deferred deep linking that works through ESP redirect chains. Not all do. Some deferred deep link solutions break when the click passes through multiple redirects before reaching the app store.

Transactional vs Promotional vs Re-Engagement: Different Deep Link Strategies

Not all email deep links should behave the same way. The link strategy should match the campaign type.

Transactional Emails

Order confirmations, shipping updates, payment receipts, account alerts. The deep link should route to the specific transaction screen.

Deep link parameters: Transaction ID, order ID, or event identifier.

Fallback behaviour: Since these go to active users, app-not-installed is rare. If it happens, the web fallback should show the transaction details rather than prompting an install.

Measurement focus: Tap-to-screen-load time. Transactional deep links should resolve in under 2 seconds.

Promotional Emails

Sale announcements, feature launches, seasonal campaigns. These target broader segments with varying engagement levels.

Deep link parameters: Campaign ID, offer code, product category, or landing screen identifier.

Fallback behaviour: For users without the app, the web fallback should mirror the promotional offer with a clear "Get the App" prompt that preserves the offer via deferred deep link.

Measurement focus: Click-to-conversion rate. Track whether the user completed the promoted action, not just whether they opened the app.

Re-Engagement Emails

Win-back campaigns, inactivity nudges, loyalty reminders. These target dormant users, many of whom may have uninstalled.

Deep link parameters: User segment, inactivity duration, personalised offer code. Flag these links as re-engagement for attribution purposes.

Fallback behaviour: Deferred deep linking is critical. The web fallback must route through the app store while preserving all context. Post-install, the app should skip standard onboarding and route directly to the re-engagement screen.

Measurement focus: Reactivation rate, not just reinstall rate. A reinstall without a subsequent session within 48 hours is not successful re-engagement. Connect this to your re-engagement attribution framework for accurate cost-per-reactivation calculation.

Measuring Email Campaign Impact on App Engagement

Most CRM teams measure email at the ESP level: sends, opens, clicks. But the metrics that matter for email-to-app campaigns happen after the click, and they require attribution data that ESPs do not provide.

The measurement funnel you should be tracking:

Level 1: ESP metrics. Sends, deliveries, opens, clicks. Necessary but insufficient.

Level 2: Deep link resolution. How many clicks successfully resolved to an app open or web fallback? A healthy resolution rate is 95%+. Below 90% signals a technical problem with redirect chains or Universal Link configuration.

Level 3: App session initiation. Of resolved clicks, how many resulted in an actual app session? For active users, target 70-85%. For re-engagement campaigns targeting dormant users, 30-50% is realistic.

Level 4: Target action completion. Of email-initiated app sessions, how many users completed the intended action? This determines actual campaign ROI.

Level 5: Downstream retention. For re-engagement campaigns, track whether reactivated users remain active at D3, D7, and D14. A single session from an email that never repeats is not successful re-engagement.

To measure levels 2 through 5, your deep linking and attribution setup needs to pass campaign identifiers from the email click through to in-app events. Platforms like Linkrunner integrate directly with MoEngage, CleverTap, and Braze, so attributed deep links can be embedded into email templates with campaign and user-level parameters that flow through to in-app event tracking automatically, closing the loop without manual data stitching.

Implementation Checklist for CRM Teams

Use this checklist to audit your current email deep link setup or plan a new implementation.

Technical Foundation

1. Verify Universal Links and App Links configuration. Confirm your apple-app-site-association and assetlinks.json files are correctly hosted, accessible, and up to date. Test with Apple's AASA validator and Google's Digital Asset Links tool.

2. Audit ESP link wrapping behaviour. Send test emails through your ESP and inspect the full redirect chain. Document how many redirects occur between the tap and your destination URL. If your ESP supports custom tracking domains or link passthrough, configure it.

3. Build a smart fallback page. Create a mobile-optimised landing page on your deep link domain that detects in-app browsers (Gmail, Outlook), displays campaign context, and offers an "Open in App" button. This page should load in under 1 second.

4. Test deferred deep linking end-to-end. Uninstall your app, click an email deep link, install from the store, and verify that the app opens to the correct screen with all parameters preserved. Test on both iOS and Android.

5. Define a consistent deep link parameter schema. Campaign ID, campaign type (transactional/promotional/re-engagement), user segment, offer code, and destination screen. Document this so every CRM team member uses the same structure.

Measurement Setup

1. Connect ESP click events to deep link resolution events. Your analytics must link an ESP click ID to the corresponding deep link open event, either through server-side event passing or shared identifiers.

2. Set up the full open-to-action funnel. Track: email opened, link clicked, app opened (with deep link source), target screen viewed, target action completed. Each event should carry the campaign identifier.

3. Configure separate re-attribution rules for email-driven reinstalls. Set re-attribution windows of 24-48 hours for re-engagement campaigns.

4. Build a deep link health dashboard. Track resolution rate, app open rate from email clicks, and action completion rate. Alert when resolution drops below 90%.

Ongoing QA

1. Test across email clients monthly. Verify deep link behaviour in Gmail (iOS/Android), Outlook (iOS/Android), Apple Mail, and Samsung Mail. Document changes after client updates.

2. Monitor ESP redirect chain changes. ESPs occasionally update link wrapping infrastructure, which can break Universal Links. Include redirect testing in your monthly QA cycle.

3. Validate deep links after app updates. New screens or changed URL handling can break routing. Include deep link validation in your app release checklist.

Frequently Asked Questions

Do deep links work in all email clients?

Not equally. Apple Mail handles Universal Links natively. Gmail and Outlook open links in their in-app browsers, which bypass Universal Link triggers. Build a smart fallback page that detects the email client and provides an "Open in App" button when direct app opening fails.

How do I track email-to-app conversions accurately?

Pass unique campaign and user identifiers through your deep link parameters. Your deep link provider should carry these into the app session as event properties, connecting the ESP click to the in-app action without probabilistic matching.

What happens when a user clicks an email deep link but the app is not installed?

With deferred deep linking, the user routes to the app store. After installation, the app receives the original parameters and routes to the intended screen. Without deferred deep linking, the user lands on the home screen with no context.

How do I handle users who have the app but are logged out?

Pass a session or authentication token hint through the deep link parameters. If the user is logged out when the app opens, show a streamlined login screen that acknowledges the email context ("Log in to view your rewards") rather than the generic onboarding flow.

Which CRM platforms support deep link integration?

MoEngage, CleverTap, and Braze all offer native integrations with attribution platforms that pass campaign context through to in-app events. Linkrunner integrates with all three, making it straightforward to embed attributed deep links directly into CRM workflows without custom engineering.

Key Takeaways

The gap between email click and app action is where most CRM campaign value disappears. The fix is infrastructure: properly configured deep links that survive ESP redirect chains, handle email client edge cases, and carry attribution data from inbox to in-app event.

Start with the technical foundation (Universal Links, App Links, smart fallback pages), then layer in measurement that tracks the full open-to-action funnel. Differentiate your deep link strategy by campaign type, and treat deferred deep linking as non-negotiable for any re-engagement programme.

The CRM teams that close this gap unlock accurate measurement of email's true contribution to app revenue, which changes how lifecycle marketing gets funded.

If your team is looking to implement attributed deep links across email and CRM workflows without building custom redirect infrastructure, request a demo from Linkrunner to see how the platform handles ESP redirect chains, deferred deep linking, and CRM integration out of the box.