Proton Mail represents a significant advancement in mobile email security, offering end-to-end encryption that ensures only senders and intended recipients can access message content. Developed by Switzerland-based Proton AG, the application leverages the country's strong privacy laws to provide an additional layer of data protection beyond its technical encryption measures. The platform has gained recognition from reputable publications including The Wall Street Journal, which noted the virtually unbreakable encryption protecting user communications. The application's core functionality includes creating @proton.me or @protonmail.com addresses, sending and receiving encrypted messages, and comprehensive inbox management. Encryption occurs automatically between Proton Mail users, while optional password-protected messages can be sent to external email addresses with expiration timers. The platform employs zero-access encryption architecture, meaning even Proton AG cannot decrypt user emails stored on their servers, providing true end-to-end protection. User experience presents both strengths and challenges. The interface maintains a clean, professional design with intuitive navigation, though some users report performance issues. Real-world usage patterns indicate the app serves particularly well for sensitive communications, business correspondence, and users seeking alternatives to data-harvesting email platforms. The Android implementation includes standard email management features alongside security-focused tools like self-destructing messages and sender verification. User feedback reveals consistent patterns across the 4.6-star rating. Mark's July 2025 review highlighted significant loading delays and message-sending failures, though subsequent updates reportedly improved performance. Elisa F's September 2025 critique focused on the mandatory conversation view, while multiple users including Sally K MiMi (August 2025) noted the learning curve for less technically-inclined users. Storage space requirements emerged as another consideration, as mentioned by Timothy Jones in September 2025. The application demonstrates clear strengths in security implementation and privacy protection, though faces challenges in performance optimization and feature customization. Ideal use cases include journalists, business professionals, activists, and any users prioritizing communication privacy. Limitations include occasional performance inconsistencies, limited interface customization options, and the learning curve associated with advanced security features. The platform represents one of the most robust mobile email security solutions available, particularly for users willing to trade some convenience for unparalleled privacy protection.