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Shawon Hossain (1809256)
Shawon Hossain (1809256)

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Why We Built an Offline-First Architecture for Temporary Emails on Android

#android #kotlin #architecture #sqlite

Why We Built an Offline-First Architecture for Temporary Emails on Android

Handling temporary inboxes on mobile is deceptively complex. Most web-based disposable email tools keep data strictly in the browser session. If the user refreshes, switches tabs, or navigates away, the inbox—and that crucial 6-digit verification code—vanishes.

When designing Mailfo, an Android disposable email client, our goal was to eliminate this friction entirely.

The Challenge: Ephemeral Yet Durable

The core paradox of a disposable email app:

  • The email address is ephemeral (discarded after use).
  • The incoming verification email is mission-critical (a user waiting for an OTP cannot afford to lose it due to a background process kill).

On Android, background webviews and tabs get aggressively reaped under memory pressure. If a user opens Chrome to submit a form, switches to their email app, and finds the inbox resetting, the signup flow is ruined.

Architectural Decision: Room Database as the Single Source of Truth

Rather than holding message payloads in runtime memory (ViewModel or state holder), we route every inbound email through a local Room SQLite database:

@Entity(tableName = "cached_messages")
data class CachedMessage(
    @PrimaryKey val id: String,
    val sender: String,
    val subject: String,
    val body: String,
    val receivedTimestamp: Long,
    val category: MessageCategory,
    val isRead: Boolean
)
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Benefits:

  1. Zero Data Loss on App Switch: Even if Android shuts down the app while you're in the browser, the OTP is sitting in SQLite when you return.
  2. Instant Local Filtering: Users can filter between All, Unread, Promotions, and Important codes instantaneously without network round-trips.
  3. True Offline Resilience: If mobile connectivity drops right after receiving the push payload, the code is still fully readable offline.

Privacy by Design

Durable storage shouldn't mean persistent tracking. Mailfo includes a 1-tap cache purge that executes DELETE FROM cached_messages and clears all local tokens.

If you're building or testing apps that involve email verification flows:

Have you built offline-first mobile apps for ephemeral workflows? What trade-offs did you encounter?

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