Reference
Push notification glossary.
62 terms across push, email, automation, deliverability, compliance, and infrastructure — written for engineers who would rather read a definition than guess.
Sections
Section
Push notifications
Terms covering web push, mobile push, payloads, and the W3C Push API.
- Web Push
- A W3C-standard delivery mechanism that lets a website send notifications to a browser even after the page is closed. The browser stores a subscription token and the server uses it to push messages without polling.
- Mobile Push
- A notification delivered to a native mobile app via a platform service (FCM on Android, APNs on iOS). The app surfaces the message on the lock screen, notification shade, or banner depending on OS settings.
- VAPID
- Voluntary Application Server Identification — a public/private key pair that proves your push messages came from your origin. Web push servers (Chrome, Firefox, Edge, Safari) require a VAPID signature on every send so subscribers know who is messaging them.
- FCM
- Firebase Cloud Messaging — Google's service for delivering pushes to Android devices and to Chrome browsers via WebPush. You upload a service-account credential once and target devices by FCM tokens.
- APNs
- Apple Push Notification service — the gateway for delivering pushes to iOS, iPadOS, and macOS devices. Authentication uses either token-based JWT (the .p8 key) or older certificate-based credentials.
- Service Worker
- A background script that the browser keeps alive after the page is closed; it listens for incoming push events and renders the notification. ReachBell ships a default service worker you copy to your site root, but you can extend it for custom click handling.
- Push Subscription
- A token that uniquely identifies a browser/device + origin pair for push delivery. The subscription contains an endpoint URL and two keys (p256dh + auth) used to encrypt the payload end-to-end.
- p256dh
- A public key generated by the browser when a user subscribes to web push, used for payload encryption via Elliptic Curve Diffie-Hellman. Combined with the auth secret, it lets push services deliver encrypted payloads the server can't read.
- Notification Payload
- The JSON sent with each push — typically title, body, icon, image, badge, actions, and arbitrary data. Web push payloads are capped at around 4 KB after encryption; mobile push limits vary by platform.
- Deep Link
- A URL inside a notification that opens a specific screen in your app or site instead of the home page. Push providers attach UTM tags and tracking IDs to the deep link so click-through attribution works out of the box.
- Silent Push
- A push with no user-visible notification, used to trigger a background app refresh or to wake the service worker. Browsers and iOS enforce strict limits on silent pushes and may revoke the subscription if abused.
- Dead Token
- A push subscription that's no longer valid because the user uninstalled the app, cleared the browser, or revoked permission. ReachBell automatically prunes dead tokens from your audience to keep deliverability metrics honest.
Section
Email & deliverability
Terms that decide whether your email lands in the inbox.
- SPF
- Sender Policy Framework — a DNS TXT record that lists which servers are allowed to send email on behalf of your domain. Receiving mailservers check the record on every inbound message; failures lower your deliverability.
- DKIM
- DomainKeys Identified Mail — a cryptographic signature added to outgoing email headers that proves the message wasn't altered in transit and came from an authorised sender. Each domain has a public key in DNS that receivers use to verify the signature.
- DMARC
- A policy that ties SPF and DKIM together and tells receiving mailservers what to do when a message fails alignment — accept, quarantine, or reject. DMARC also publishes a reporting address so you can see who's spoofing your domain.
- Bounce
- A non-delivery report from a receiving server. Hard bounces (invalid mailbox) should suppress the address permanently; soft bounces (full mailbox, server down) are retried for a few days before being marked.
- Complaint
- A "mark as spam" report fired by a recipient. Even a small complaint rate (~0.1%) damages sender reputation; ReachBell auto-suppresses complainers and surfaces complaint rate per campaign.
- Transactional Email
- A message triggered by a user action — receipt, password reset, magic link, invite. Transactional sends bypass marketing throttles, ignore quiet hours, and have stricter latency requirements (seconds, not minutes).
- Marketing Email
- A broadcast or campaign send to a list of opted-in recipients, subject to frequency caps, quiet hours, and one-click unsubscribe. Marketing email is the bulk of volume and carries most of the deliverability risk.
- Deliverability
- The probability that an email lands in the inbox rather than spam or the bin. It depends on sender reputation, authentication (SPF/DKIM/DMARC), list hygiene, content quality, and engagement signals.
- List Hygiene
- The practice of keeping your subscriber list clean by removing bounced, complained, and inactive addresses. A clean list improves deliverability because mailbox providers measure engagement per send.
- Open Rate
- The percentage of delivered emails that triggered the tracking pixel — i.e. were rendered by an email client. Apple Mail Privacy Protection pre-loads images for many users, so open rate has become a fuzzy signal rather than a hard one.
- Click-Through Rate
- The percentage of delivered emails (or pushes) that produced a click on a tracked link. CTR is the most reliable engagement signal because it requires deliberate action, not just rendering.
- Sender Reputation
- A score that mailbox providers (Gmail, Outlook, Yahoo) assign to each sending IP and domain based on engagement, complaints, bounce rate, and authentication. Reputation moves slowly — gain it with consistent sending, lose it with one bad blast.
Section
Identifiers & authentication
Keys, tokens, and identifiers that make the messaging stack secure.
- API Key
- A secret string that identifies your project to the ReachBell REST API. Keys are scoped per project (and optionally per environment) so a leaked staging key can't broadcast to production subscribers.
- Webhook Signing Secret
- A shared secret used to sign outbound webhooks (HMAC-SHA256). Your server verifies the signature before processing the payload so attackers can't forge events to your endpoint.
- Idempotency Key
- A unique identifier you attach to a request so retries don't cause duplicate sends. ReachBell's send endpoints cache the result by key for 24 hours; the second call returns the cached response without re-sending.
- Subscriber ID
- The stable identifier ReachBell uses for a subscriber. You can also supply your own external_id (e.g. your database user id) so events sent from your backend resolve to the right subscriber.
- External ID
- Your internal user identifier (UUID, integer, email) stored on the ReachBell subscriber so events from your backend can be mapped without a lookup. Useful for de-duplicating multiple device tokens that belong to the same user.
- Tag
- A free-form label attached to a subscriber (e.g. `plan:pro`, `lang:hi`). Tags are the building block of segments and let you target users without rewriting database queries.
- OAuth Scope
- A permission string attached to an OAuth token that limits what the holder can do — e.g. `messages:send` but not `subscribers:export`. Scopes let you give a third-party integration only the access it needs.
Section
Compliance & privacy
Regulations and patterns that keep your messaging legal.
- Opt-In
- A subscriber's explicit consent to receive messages on a given channel. ReachBell records the opt-in event, source, timestamp, and IP so you can prove consent to a regulator if asked.
- Double Opt-In
- A two-step consent flow where a subscriber signs up, then confirms via a link in their inbox before being added to the list. It raises list quality and is required by some regulators for email marketing.
- Soft Prompt
- A custom UI shown before the browser's native push permission dialog. A soft prompt asks "Want updates?" with a Yes/No so users who say no don't burn the native permission, which the browser then permanently blocks.
- One-Click Unsubscribe
- A regulation-mandated link in every marketing email that removes the subscriber in a single click — no login, no form. Email providers (Gmail, Yahoo) now require list-unsubscribe-post for senders above a certain volume.
- Preference Center
- A hosted page where subscribers can pick which channels and topics they receive. ReachBell's preference centre is generated per subscriber and updated instantly across every campaign.
- GDPR
- The EU's General Data Protection Regulation. It governs processing of personal data of EU residents — including consent requirements, data-subject access rights, and breach-notification timelines. Penalties reach 4% of global revenue.
- DPDP Act
- India's Digital Personal Data Protection Act, 2023. It introduces consent requirements, purpose limitation, and data fiduciary obligations for processing the personal data of Indian residents.
- CAN-SPAM
- US legislation governing commercial email — requires accurate from-addresses, a clear unsubscribe mechanism, and a physical postal address in every marketing email. Violations carry penalties up to $50,120 per email.
- Audit Log
- A timestamped record of every administrative action — campaign sent, segment edited, key revoked, subscriber exported. ReachBell retains audit logs for 90 days on Growth and above; the log is exportable.
- Data Retention
- How long a vendor stores subscriber data, events, and message bodies. ReachBell retains delivery events for 90 days, message bodies for 30 days, and offers a "delete on cutover" option for migrations.
Section
Engagement & growth
Segmentation, testing, and the metrics that matter.
- Segment
- A reusable filter that resolves to a set of subscribers — e.g. "users in India who clicked a push in the last 7 days". ReachBell evaluates segments at send time so campaigns always target the freshest data.
- Automation (Flow)
- A visual workflow of sends, waits, and conditional branches triggered by a subscriber event. A flow runs per-subscriber and can exit early on user actions (e.g. order placed, trial converted).
- A/B Testing
- Splitting a campaign into two variants (A and B) sent to deterministically-bucketed sub-audiences, then promoting the winner by a defined metric — usually click-through rate. ReachBell can auto-promote after a configurable hold period.
- Frequency Cap
- A per-subscriber limit on how many marketing messages can be sent over a given window — e.g. max 2 pushes per day. Capped sends are skipped, not failed, so the audit log records the would-have-sent for compliance.
- Quiet Hours
- A project-wide window during which marketing sends are paused — typically 22:00–07:00 in each subscriber's timezone. Quiet hours respect the user even when your timezone is different.
- Throttling
- Deliberately limiting the send rate of a campaign to protect downstream infrastructure (your site, your support team) and to spread out delivery so deliverability metrics don't spike.
- Channel Waterfall
- A fallback chain — try push first; if no click after N minutes, send email; if email also unopened, send SMS. The waterfall avoids sending the same content twice while still reaching the user.
- Conversion
- A user action that's the goal of the campaign — purchase, signup, trial-to-paid, content view. ReachBell ties conversions back to the message that caused them via tracked deep links and event correlation.
- Cohort Retention
- The percentage of users who came in on a given date and are still active N days later. Cohort retention is the cleanest signal of whether onboarding works — if day-7 retention is bad, no engagement layer will fix it.
- Merge Tag
- A token in a template like `{{first_name}}` that gets replaced with subscriber-specific data at send time. Merge tags pull from subscriber traits, event payloads, or segment metadata.
Section
Infrastructure & security
Backend, security, and operational vocabulary.
- Webhook
- An HTTP POST your application sends to a registered URL when something happens (cart abandoned, post published). ReachBell can both receive webhooks (as a trigger) and emit them (on delivery, click, bounce).
- IDOR
- Insecure Direct Object Reference — a class of authorization bug where an attacker can access another tenant's data by guessing or modifying object IDs in a URL. ReachBell uses opaque IDs and tenant-scoped queries to make IDOR practically impossible.
- Rate Limit
- A cap on how many API calls a key can make per window (typically per second and per minute). ReachBell returns standard rate-limit headers so SDKs can back off automatically without burning quota.
- CDN
- Content Delivery Network — a globally distributed cache that serves static assets close to the user. ReachBell's opt-in prompt and service worker are served from a CDN so they load in milliseconds anywhere.
- Encryption at Rest
- Storing data on disk in encrypted form so a stolen disk reveals nothing. ReachBell encrypts subscriber data, message bodies, and audit logs at rest with AES-256.
- TLS
- Transport Layer Security — the protocol that encrypts traffic between your browser/app and a server (the S in HTTPS). ReachBell only accepts inbound traffic over TLS 1.2+; web push requires HTTPS on your origin.
- HMAC
- Hash-based Message Authentication Code — a way to prove a payload was created by someone with the shared secret. ReachBell signs every webhook with HMAC-SHA256 so your server can verify authenticity before processing.
- Queue
- A FIFO buffer of pending sends. ReachBell's send pipeline queues messages, retries failures with exponential backoff, and marks them dead-letter only after configurable retry attempts so transient errors don't lose messages.
- Dead-Letter Queue (DLQ)
- A queue for messages that failed all retry attempts. DLQ entries are surfaced in the dashboard with the original payload and error so the operator can investigate without re-running the campaign.
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