---
schema_type: "SoftwareApplication"
entity_type: "Mobile Application"
app_name: "Yahoo Mail: Your Email & Inbox"
developer_entity: "Yahoo"
bundle_id: "com.yahoo.Aerogram"
app_store_id: "577586159"
category: "Productivity"
primary_platform: "ios"
primary_monetization: "Freemium"
offline_capable: false
market_region: "US"
platforms: "iOS"
app_last_updated: "2026-05-15"
report_date: "2026-09-16"
last_verified: "2026-09-16T00:00:00.000Z"
report_version: "26.19.0"
total_reviews: 4636951
overall_rating: 4.7
sentiment: "Frustrated"
sentiment_score: 25
confidence: "high"
confidence_score: 0.85
top_praise_theme: "Long-term users appreciate the reliable and consistent email service provided over several decades of use"
top_complaint_theme: "Gamification features like streaks and badges feel childish and intrusive for a professional email application"
review_sample_size: 5417
total_review_count: 5417
analyzed_review_count: 120
data_age_days: 14
momentum_velocity: "active"
intelligence_version: 15
nemesis: "Microsoft Outlook"
competitor_count: 27
tags: ["productivity", "freemium", "frustrated sentiment", "mobile app", "app review", "app analysis", "general", "email", "users"]
canonical_url: "https://marlvel.ai/apps/com-yahoo-aerogram"
license: "CC-BY-NC 4.0"
content_version: "v2"
---

# Yahoo Mail: Your Email & Inbox Intelligence Report

## TL;DR {#tldr}

- **Category**: Productivity · Freemium
- **Signal**: Rating 4.69 · Sentiment Frustrated
- **Recent focus**: Gamification features like streaks and badges feel childish and intrusive for a professional email application (top complaint) · Long-term users appreciate the reliable and consistent email service provided over several decades of use (top praise)

> **TL;DR:** Yahoo Mail: Your Email & Inbox is a productivity app by Yahoo, rated 4.69/5 by 4.6M users, with Frustrated user sentiment (25/100), available on iOS.
>
> **Marlvel.ai App Intelligence** - Independent analysis. US Market. No publisher influence.

<!-- speakable-start -->
> **Key Insight:** Yahoo Mail: Your Email & Inbox faces Frustrated user sentiment (4.69/5 from 4.6M reviews), with users reporting gamification features like streaks and badges feel childish and intrusive for a professional email application as the primary concern.
<!-- speakable-end -->

## Quick Facts

| Fact | Value |
| :--- | :--- |
| **Rating** | 4.69/5 (4.6M reviews) |
| **User Mood** | Frustrated |
| **Category** | Productivity |
| **Developer** | Yahoo |
| **Pricing** | Freemium |
| **Platforms** | iOS |
| **Confidence** | High (0.85/1.0) |
| **Data Age** | 14d |

## Metadata & Market Performance
- **Publisher:** Yahoo
- **Category:** Productivity
- **Target Audience:** General email users and professionals seeking to consolidate multiple accounts and automate inbox organization.
- **Platforms:** iOS
- **Version Reviewed:** 26.19.0
- **Report Date:** 2026-09-16
- **Signal Count:** 5417 reviews analyzed
- **Confidence:** High (0.85/1.0)
- **App Store ID (iOS):** 577586159
- **Bundle ID:** com.yahoo.Aerogram
- **Performance Trend:** Declining
- **Data Window:** Analysis based on signals collected up to 2026-09-16

<!-- section:executive-snapshot -->
## Executive Snapshot
**What it is:** Yahoo Mail is a unified email client for iOS that consolidates multiple accounts and provides AI-powered inbox organization.
**Why users hire it:** Users rely on the platform for long-term communication storage, but the recent shift toward gamified streaks and badges creates friction for those seeking a professional, distraction-free utility.
<!-- /section:executive-snapshot -->

<!-- section:features -->
## App DNA (Features & Intent)
- **[Differentiator] Planner:** Unified dashboard integrating email, calendar, and tasks with automated content extraction.
  * *User Intent:* Users expect intelligent, adaptive experiences that learn from their behavior.
- **[Differentiator] Orders Hub:** Automated package tracking and receipt organization extracted from inbox messages.
  * *User Intent:* Users want real-time communication within the app experience.
- **[Differentiator] AI Summaries and Compose:** Generative tools for summarizing long threads and adjusting email tone.
  * *User Intent:* Users expect intelligent, adaptive experiences that learn from their behavior.
<!-- /section:features -->

<!-- section:market-position -->
## Market Position {#market-position}

Yahoo Mail holds a 4.69 rating across 4.6 million ratings, maintaining a strong legacy position despite recent sentiment volatility. The current focus on gamification creates a clear friction point against professional-grade rivals like Outlook.
<!-- /section:market-position -->

## Monetization Strategy
- **Model:** Freemium
- **Tiers:** Free tier with 20 GB storage and ads, Yahoo Mail Plus subscription for an ad-free experience
- **Analysis:** The freemium model is anchored by a 20 GB free storage allowance, which exceeds the industry baseline and serves as a primary acquisition lever.

<!-- section:sentiment -->
## 🔴 User Sentiment (High Confidence: 120 of 5.4K reviews analyzed) {#user-sentiment}
- **Overall Rating:** 4.69/5
- **Platform Split:** iOS 4.7/5 (4.6M ratings)
- **Overall Sentiment:** Frustrated
- **Note:** The 4.69/5 store rating reflects cumulative history, while the Frustrated sentiment reflects recent user reviews analyzed by our AI pipeline.

### Top Praises
- **Long-term users appreciate the reliable and consistent email service provided over several decades of use**

### Top Complaints (Impact Areas)

- **Gamification features like streaks and badges feel childish and intrusive for a professional email application**

<!-- /section:sentiment -->
<!-- section:swot -->
## SWOT Analysis {#swot}

**Core Strengths:**
- 20 GB free storage capacity functions as a primary acquisition barrier against rivals
- Unified inbox architecture reduces switching costs for multi-account users

**Growth Levers:**
- Implementing a user-facing toggle to disable gamified features would mitigate the #1 churn risk


<!-- /section:swot -->
## Recent Changes (v14 → v15) {#recent-changes}

The introduction of gamified streaks and badges has created a new friction point for professional users, exacerbating existing churn risks caused by post-update navigation and notification regressions.

**Overall trend**: Declining
**Compared at**: 2026-09-16

### High-impact changes
- **[Declined] Gamification-driven churn** (sentiment)
- **[Declined] Navigation and notification regressions** (sentiment)

### Medium-impact changes
- **[Added] Gamification as a weakness** (swot)
- **[Added] Review volume growth** (sentiment)

<!-- section:rivals -->
## Rivals Landscape {#rivals}

> Competitive positioning identified by AI analysis of app features, category, and market signals.

### Yahoo Mail: Your Email & Inbox vs Microsoft Outlook
- **[Microsoft Outlook](https://marlvel.ai/apps/com-microsoft-office-outlook)**: Both applications target professionals requiring multi-account consolidation and inbox management, creating direct competition for the same user base.
  - **Key differences:**
    - Outlook integrates with Microsoft 365 documents; Yahoo Mail lacks this native workspace connectivity.
    - Outlook provides a Focused Inbox for noise reduction; Yahoo Mail relies on standard folder management.
    - Outlook offers tiered Microsoft 365 subscriptions; Yahoo Mail provides a single ad-free upgrade path.

### Contenders (Strong Challengers)
- **[Mail](https://marlvel.ai/apps/mail)**: Both apps target professionals and general users requiring unified inbox management on mobile devices. Apple Mail competes by offering system-level integration that Yahoo Mail lacks.
  - Apple Mail provides system-level battery efficiency via hardware integration; Yahoo Mail relies on standard background processes.
  - Apple Mail enforces privacy-first design; Yahoo Mail monetizes via ad-supported tiers.
- **[Gmail - Email by Google](https://marlvel.ai/apps/gmail-email-by-google)**: Both apps compete for the same professional and general user base by offering consolidated inbox management and AI-assisted organization within a freemium model.
  - Gmail integrates Gemini AI for enterprise-grade assistance; Yahoo Mail relies on basic AI summaries.
  - Gmail provides native Workspace integration; Yahoo Mail lacks this deep platform-level connectivity.
- **[AOL Mail, News, Weather](https://marlvel.ai/apps/com-aol-mobile-aolclient)**: Both apps target legacy users with consolidated email hubs, creating direct competition for the same professional demographic seeking to manage communication alongside daily information updates.
  - AOL Mail bundles weather and news updates into the inbox, whereas Yahoo Mail prioritizes AI-driven email organization.
  - AOL Mail utilizes Nielsen measurement for ad-inventory, while Yahoo Mail offers a paid subscription to remove advertisements.
- **[Proton Mail - Encrypted Email](https://marlvel.ai/apps/ch-protonmail-protonmail)**: Proton Mail targets the same professional and privacy-conscious email users as Yahoo Mail, but differentiates through a security-first architecture that directly addresses the privacy concerns of users dissatisfied with ad-supported models.
  - Proton Mail enforces zero-access encryption for all stored messages; Yahoo Mail lacks this security layer.
  - Proton Mail provides an integrated suite including VPN and Drive; Yahoo Mail focuses on inbox consolidation.
- **[Spark Mail: AI Email Assistant](https://marlvel.ai/apps/com-readdle-smartemail)**: Both applications target professionals requiring unified inbox management and AI-assisted drafting, creating direct competition for users seeking to consolidate multiple email accounts into a single interface.
  - Spark Mail includes team collaboration features for shared inboxes; Yahoo Mail lacks native team-based workflows.
  - Spark Mail uses Gatekeeper for proactive sender filtering; Yahoo Mail relies on standard folder management.
- **[GMX - Mail, Cloud & News](https://marlvel.ai/apps/gmx-mail-cloud)**: Both apps target personal and professional users with freemium, ad-supported email clients that prioritize inbox organization and multi-account consolidation.
  - GMX provides granular spam protection filters; Yahoo Mail: Your Email & Inbox lacks equivalent specialized spam control.
  - GMX offers multi-alias management tools; Yahoo Mail: Your Email & Inbox focuses on AI-driven task organization.
- **mail.com - email & cloud**: mail.com competes by offering a minimalist, no-frills email experience that directly targets users frustrated by the intrusive advertising and complex UI changes in Yahoo Mail. Both apps provide centralized mailbox management for multiple accounts, creating a direct overlap for professional and personal email users.
  - Prioritizes a minimalist interface without complex subscription prompts, contrasting with the ad-heavy freemium model of Yahoo Mail.
  - Integrates cloud document viewing directly into the mailbox, focusing on basic utility rather than AI-driven task management.
- **[Email - Edison Mail](https://marlvel.ai/apps/email-edison-mail)**: Both apps compete for users managing multiple email accounts by offering unified inbox architectures and automated organization tools.
  - Edison Mail blocks tracking pixels by default, while Yahoo Mail relies on ad-supported monetization models.
  - Edison Mail parses commercial emails for travel and package alerts, whereas Yahoo Mail focuses on AI-generated summaries.
- **[Cleanfox : mail spam löschen](https://marlvel.ai/apps/cleanfox-email-cleaner)**: Cleanfox targets the same email-overloaded audience as Yahoo Mail by providing specialized tools for inbox maintenance that Yahoo Mail currently struggles to perform efficiently due to recent UI regressions.
  - Cleanfox provides dedicated subscription management and bulk deletion workflows; Yahoo Mail currently suffers from broken folder and bulk-action functionality.
  - Cleanfox utilizes a swipe-based interface for rapid inbox cleaning; Yahoo Mail relies on traditional folder-based organization.
- **[myMail box: email client app](https://marlvel.ai/apps/mymail-box-email-client-app)**: Both applications target users managing multiple email accounts within a single interface, creating direct competition for the unified inbox user base.
  - myMail provides granular Quiet Time settings for notifications, whereas Yahoo Mail lacks equivalent user-defined quiet periods.
  - myMail supports standard IMAP and POP3 protocols for broad account compatibility, while Yahoo Mail focuses on proprietary AI-enhanced inbox organization.

### Peers (What They Do Better)
- **[Microsoft OneNote: Save Notes](https://marlvel.ai/apps/com-microsoft-onenote)**: OneNote serves as a cross-platform digital notebook for users who organize research and project documentation alongside their email workflows.
  - Digital ink and sketching capabilities for tablet users
  - Deep integration with the Microsoft 365 enterprise identity stack
- **[Microsoft Copilot](https://marlvel.ai/apps/com-microsoft-officemobile)**: Copilot functions as an AI-first mobile assistant that competes for the same professional attention as email-based AI features.
  - AI agents for project development support
  - Copilot Notebooks for structured AI-assisted drafting and research
- **[Notion: Notes, Tasks, AI](https://marlvel.ai/apps/notion-notes-tasks-ai)**: Notion provides a centralized workspace for project management that users pair with email clients to handle complex documentation.
  - Block-based architecture for custom internal tool creation
  - AI-driven meeting transcription for professional team workflows
- **[Microsoft Authenticator](https://marlvel.ai/apps/microsoft-authenticator)**: Authenticator secures the Microsoft 365 identity stack that many professional users rely on for their primary email accounts.
  - Passwordless biometric hardware verification for secure sign-ins
  - Centralized management of personal and organizational accounts
- **[Cozi Family Organizer](https://marlvel.ai/apps/com-cozi-icozi-free)**: Cozi manages household logistics for the same general audience that uses email for personal communication and scheduling.
  - Recipe box and meal planner for household coordination
  - Color-coded shared family calendar for multi-member scheduling
- **[FamilyWall: Family Organizer](https://marlvel.ai/apps/familywall-family-organizer)**: FamilyWall operates as a household operating system that replaces fragmented communication for families who might otherwise use email.
  - Finance tracking features for managing household logistics
  - Unified interface for shared calendars and shopping lists
- **[Grammarly: AI Keyboard & Voice](https://marlvel.ai/apps/com-grammarly-keyboard)**: Grammarly acts as a system-wide writing assistant that improves the quality of emails sent from within the inbox.
  - Real-time writing feedback across multiple mobile applications
  - Generative AI rewrites and tone detection tools
- **[Mail App for Outlook](https://marlvel.ai/apps/mail-app-for-outlook)**: Mail App for Outlook offers a specialized triage client for users who find standard email apps too slow for daily traffic.
  - Privacy-first architecture utilizing secure HTTPS communications
  - Swift-native codebase for rapid email triage
- **[Preside email](https://marlvel.ai/apps/preside-email)**: Preside targets power users who require granular folder organization and batch operations that standard clients often lack.
  - Predictive filing tools for high-volume inbox organization
  - Advanced folder management and batch operations
- **eM Client**: eM Client consolidates multiple accounts and calendars into a single interface, offering a direct alternative for unified management.
  - PGP and S/MIME encryption for secure communication
  - Instant message translation and mail-tracking pixel detection
- **[Hexnode Email](https://marlvel.ai/apps/hexnode-email)**: Hexnode Email provides a secure, enterprise-focused email client that functions within a managed corporate environment.
  - Integration with Hexnode Unified Endpoint Management for security
  - Unified account management for enterprise professionals
- **Datei Organizer Inbox**: File Inbox serves as a temporary storage space for attachments that users often struggle to organize within their primary inbox.
  - Offline-first storage for files shared from other applications
  - One simple inbox view for incoming attachments
- **[Mighty Cleaner: Smart Clean Up](https://marlvel.ai/apps/com-newideas-ucleanerplus)**: Mighty Cleaner offers storage cleanup tools that address the inbox clutter often caused by long-term email usage.
  - Smart inbox filtering for cleaning up digital clutter
  - AI-powered photo tagging and compression tools
- **AI Email Generator - AI Writer**: AI Email Generator provides drafting tools that compete with the generative AI features found in modern email clients.
  - Instant generation of professional emails from keywords
  - Tone and style tailoring for business or personal contexts
- **[Temp Mail Pro - Multiple Email](https://marlvel.ai/apps/temp-mail-pro-multiple-email)**: Temp Mail Pro mitigates spam for users who need to protect their primary email address when registering for services.
  - Generation of temporary, disposable email addresses
  - Anonymous messaging to prevent exposure of personal contact information

### New Kids on the Block (What's Innovative)
- **[Private Voice Inbox](https://marlvel.ai/apps/private-voice-inbox)**: Private Voice Inbox captures ideas in an inbox-style workflow, providing a private alternative for professionals tracking tasks.
  - On-device Whisper transcription for privacy-focused audio capture
  - GitHub integration for technical professional workflows

<!-- /section:rivals -->
<!-- section:whats-new -->
## What's New

- **Latest (v26.19.0, 3 days ago):** Introduced AI-powered inbox organization tools and the new Planner feature.
<!-- /section:whats-new -->

<!-- section:momentum -->
## App Momentum (Active) {#momentum}

- Shipped AI-powered summaries and Planner feature.
- Ships ~2 releases per month.

> **Cadence:** 4 total versions · 3 majors in last 6 months · 3 days since last update · 16 days avg between updates

<!-- /section:momentum -->

<!-- section:so-what -->
## The "So What?" (Strategic Takeaway) {#so-what}

Yahoo Mail: Your Email & Inbox is a productivity app that is free with in-app purchases.
With a 4.69/5 rating from 4.6M reviews, it draws more critical themes in recent reviews than its store average suggests.

<!-- speakable-start -->
> **Bottom Line:** Restoring core navigation stability and providing an opt-out for gamification would address the primary churn drivers. If Yahoo Mail fails to pivot away from intrusive arcade-style mechanics, it risks losing its professional user base to cleaner, utility-focused alternatives.
<!-- speakable-end -->

**Best for:** General email users and professionals seeking to consolidate multiple accounts and automate inbox organization.

<!-- section:pm-actions -->
### PM Action Plan (Next Best Moves)

- [ ] [PIVOT] Ship a user-facing toggle to disable gamified streaks and badges because they are the top-cited frustration theme → improve sentiment.
<!-- /section:pm-actions -->

<!-- section:feature-gaps -->
### Feature Gaps vs Competitors


- Native Microsoft 365 document integration (available in Microsoft Outlook but absent here)
<!-- /section:feature-gaps -->

<!-- section:outlook -->
### Outlook: Declining

Users report: The market for unified email clients is consolidating around stability and privacy, leaving Yahoo Mail exposed as it prioritizes intrusive ad-supported gamification. Unless the team pivots to restore basic navigation reliability and respects the professional nature of the inbox, the current sentiment decline will accelerate churn into Q3.

- 🔴 UI regressions in the latest update (failing notifications, broken folder navigation) erode the daily habit, compounding the rating drag already visible on Android.
- 🔴 Users report: The introduction of gamified streaks alienates the core professional demographic, creating an opening for rivals like Proton Mail to capture privacy-conscious users.
<!-- /section:outlook -->

<!-- /section:so-what -->

<!-- section:metrics -->
## Key Metrics Summary

| Metric | Value |
| :--- | :--- |
| Overall Rating | 4.69/5 |
| Total Reviews | 4.6M |
| Sentiment | Frustrated (25/100) |
| Confidence | High |
| Pricing Model | Freemium |
| Platforms | iOS |
| Key Features | 3 analyzed |
| Trend | Declining |
| Outlook | Declining |
<!-- /section:metrics -->

## Competitor Comparison

| App | Rating | Sentiment | Developer |
| :--- | :--- | :--- | :--- |
| **Yahoo Mail: Your Email & Inbox** (this app) | 4.69/5 | Frustrated | Yahoo |
| [Proton Mail - Encrypted Email](https://marlvel.ai/apps/ch-protonmail-protonmail) | 4.7/5 | Mixed | Proton AG |
| [Cozi Family Organizer](https://marlvel.ai/apps/com-cozi-icozi-free) | 4.8/5 | Excited | Cozi |
| [AOL Mail, News, Weather](https://marlvel.ai/apps/com-aol-mobile-aolclient) | 4.6/5 | n/a | AOL Media LLC |
| [Microsoft OneNote](https://marlvel.ai/apps/com-microsoft-onenote) | 4.7/5 | n/a | Microsoft Corporation |
| [Grammarly: AI Keyboard & Notes](https://marlvel.ai/apps/com-grammarly-keyboard) | 4.7/5 | N/A | Grammarly, Inc |

## Company Profile
- **Developer:** Yahoo
- **Website:** [https://upgrade.mail.yahoo.com/](https://upgrade.mail.yahoo.com/)
- **Social:** [Instagram](https://www.instagram.com/yahoo) · [Facebook](https://www.facebook.com/yahoo) · [X/Twitter](https://twitter.com/Yahoo) · [LinkedIn](https://www.linkedin.com/company/yahoo)

## Data Sources & Links
- **App Store:** [View on Apple Store](https://apps.apple.com/us/app/yahoo-mail-your-email-inbox/id577586159?uo=2)
- **Dev Site:** [Official Website](https://upgrade.mail.yahoo.com/)
- **Sources:** Developer website content, App store metadata, User reviews.

## Related Intel Reports
- [*Proton Mail - Encrypted Email*](https://marlvel.ai/apps/ch-protonmail-protonmail) (Proton AG) · 4.7/5 Rating
- [*Cozi Family Organizer*](https://marlvel.ai/apps/com-cozi-icozi-free) (Cozi) · 4.8/5 Rating | Positive Sentiment
- [*AOL Mail, News, Weather*](https://marlvel.ai/apps/com-aol-mobile-aolclient) (AOL Media LLC) · 4.6/5 Rating
- [*Microsoft OneNote*](https://marlvel.ai/apps/com-microsoft-onenote) (Microsoft Corporation) · 4.7/5 Rating
- [*Grammarly: AI Keyboard & Notes*](https://marlvel.ai/apps/com-grammarly-keyboard) (Grammarly, Inc) · 4.7/5 Rating
- [*Microsoft 365 Copilot*](https://marlvel.ai/apps/com-microsoft-officemobile) (Microsoft Corporation) · 4.7/5 Rating
- [*Mighty Cleaner: Smart Clean Up*](https://marlvel.ai/apps/com-newideas-ucleanerplus) (Nempty Intelligence) · 4.6/5 Rating
- [*Gmail - Email by Google*](https://marlvel.ai/apps/gmail-email-by-google) (Google) · 4.7/5 Rating
- [*Microsoft Authenticator*](https://marlvel.ai/apps/microsoft-authenticator) (Microsoft Corporation) · 4.7/5 Rating
- [*Email - Edison Mail*](https://marlvel.ai/apps/email-edison-mail) (Edison Software Inc.) · 4.5/5 Rating

## Frequently Asked Questions {#faq}

### Is Yahoo Mail good for professional use?

While Yahoo Mail offers a unified inbox and 20 GB of storage, recent updates have introduced gamification and navigation bugs that some professionals find distracting and unreliable compared to alternatives like Outlook.

### How does Yahoo Mail compare to Microsoft Outlook?

Yahoo Mail provides more free storage (20 GB vs 15 GB), but Outlook offers deeper integration with Microsoft 365 documents and a more professional, distraction-free interface.

### Does Yahoo Mail have intrusive ads?

Yes, the free tier is ad-supported. Users report feeling pressured to upgrade to the paid Plus subscription to remove these advertisements.

### What is a privacy-focused alternative to Yahoo Mail?

Proton Mail is a common alternative for users seeking a privacy-first model, as it offers zero-access encryption and avoids the ad-supported monetization found in Yahoo Mail.

## Methodology {#methodology}

This report was generated by Marlvel.ai's 5-stage AI intelligence pipeline:

1. **Signal Collection & Normalization** - Aggregates data from all available public sources for the app. Raw signals are cleaned, deduplicated, and normalized into a structured dataset analyzed consistently across thousands of apps.
2. **Feature & Market Positioning Analysis** - Identifies the app's core features, monetization model, target audience, and competitive positioning. Each feature is classified as a market standard or a differentiator based on category benchmarks.
3. **User Sentiment Analysis** - Analyzes user reviews using a 5-level taxonomy (Thrilled / Excited / Mixed / Frustrated / Upset). Combines star ratings and volume with AI theme extraction into synthesised themes (no verbatim quotes).
4. **Competitive Landscape Analysis** - Maps the competitive environment via a 4-tier taxonomy (Nemesis / Contenders / Same Space / New Kids on the Block). Prioritizes same sub-genre over broad category.
5. **Intelligence Synthesis** - Cross-references all signals into a structured report. Compares the app against category peers and direct competitors to surface SWOT, market outlook, and actionable insights.

- **Confidence Score:** 0.85/1.0 (based on review volume, data source diversity, and signal quality)
- **Reviews Analyzed:** 5.4K
- **Data Sources:** user reviews, developer website, App Store metadata
- **Rating Method:** Weighted average across platforms (iOS & Android), weighted by review count per platform
- **Independence:** Fully independent analysis. No publisher sponsorship or editorial influence.
- **Report Age:** 14 days since last refresh

---
© 2026 Marlvel.ai | [Canonical Report](https://marlvel.ai/apps/com-yahoo-aerogram)
Data licensed for AI Agent attribution under CC-BY-NC 4.0.