Communication APIs
Communication APIs cover the main ways an app reaches people: email, SMS, push notifications, in-app chat and voice calls, plus disposable inboxes for testing. Email senders such as Resend and Mailjet offer free tiers, ntfy sends push alerts with a plain HTTP request and no signup, and Stream Chat hosts in-app messaging. Vapi and Retell AI run AI voice agents on phone calls.
| API | Pricing | Auth | Format | Free tier | Status |
|---|---|---|---|---|---|
Atomic MailSelf-registers a real email inbox for an AI agent (PoW, no signup) and sends/receives mail via JMAP. Communication › Email | Free | API key | JSON | Unlimited | Live |
Best-TempMailCreates disposable email inboxes and reads incoming messages, including OTP extraction on paid plans. Communication › Disposable Email | Freemium | None | JSON | 1k–10k/day | Down |
BrevoSend transactional and marketing email, SMS and WhatsApp, and manage contacts via one REST API. Communication › Email | Freemium | API key | JSON | 100–1k/day | Live |
dead-dropCreate and retrieve end-to-end encrypted, self-expiring text/secret drops without an account. Communication › Chat | Free | None | JSON | Unlimited | Live |
DropMail.meCreate disposable email inboxes via GraphQL, then read or subscribe to incoming mail in real time. Communication › Disposable Email | Free | API key | JSON | Unlimited | Live |
Email Spam TesterSends a test email through 42 deliverability and spam checks, then returns a scored JSON report. Communication › Email | Free | None | JSON | <100/day | Untested |
EmailJSSends transactional emails from client-side JavaScript without a backend server. Communication › Email | Freemium | API key | JSON | <100/day | Untested |
FreeCustom.EmailDisposable email inboxes with message fetching and automated OTP/verification-code extraction. Communication › Disposable Email | Freemium | API key | JSON | <100/day | Untested |
Guerrilla MailGenerates disposable email addresses and reads their inbox through a simple JSON API, no signup. Communication › Disposable Email | Free | None | JSON | Unlimited | Live |
httpSMSTurns your own Android phone into a controllable SMS gateway you call over HTTP. Communication › SMS | API key | JSON | — | Untested | |
ImprovMXManages email forwarding aliases and SMTP sending credentials for a custom domain. Communication › Email | Freemium | API key | JSON | 10k+/day | Live |
inboxsinkCreates disposable inboxes and blocks until a message arrives, extracting OTP codes for test automation. Communication › Disposable Email | Freemium | API key | JSON | <100/day | Live |
IndiePitcherSends transactional emails with markdown support and manages contact lists for SaaS apps Communication › Email | Freemium | API key | JSON | <100/day | Live |
mail.tmCreates disposable inboxes and lets apps poll or fetch mail sent to them, no signup needed. Communication › Disposable Email | Free | API key | JSON | Unlimited | Live |
MailjetTransactional and marketing email sending, contact list management, and delivery stats via REST API. Communication › Email | Freemium | API key | JSON | 100–1k/day | Live |
MailsacDisposable email inboxes for QA/testing: read, search and validate mail via API, webhooks or websocket. Communication › Disposable Email | Freemium | API key | JSON | <100/day | Live |
MailtrapTransactional and bulk email sending API with a built-in sandbox for safely testing emails. Communication › Email | Freemium | API key | JSON | 100–1k/day | Untested |
NotilifySends transactional SMS (OTPs, alerts) via API with delivery tracking and webhook status updates. Communication › SMS | Paid | API key | JSON | — | Live |
ntfySend push notifications to phones and desktops with a plain HTTP PUT/POST to a topic; no signup needed. Communication › Push | Freemium | None | JSON | 100–1k/day | Live |
OneSignalSend push, email, SMS and in-app messages from one REST API, with segmentation and delivery data. Communication › Push | Freemium | API key | JSON | — | Untested |
Plivo SMS APISend and receive SMS and MMS worldwide, with delivery reports and message logs; per-message US pricing. Communication › SMS | Free trial | API key | JSON | — | Live |
PostStackEU-hosted transactional and marketing email sending with templates, broadcasts and webhooks. Communication › Email | Freemium | API key | JSON | 100–1k/day | Live |
Pusher BeamsSends push notifications to iOS, Android and web apps via device interests or authenticated users. Communication › Push | Freemium | API key | JSON | — | Untested |
Pusher ChannelsManaged realtime pub/sub messaging with presence channels for live dashboards, chat, and activity feeds. Communication › Chat | Freemium | Other | JSON | 10k+/day | Untested |
PushoverSend push alerts to iOS, Android and desktop with priorities, sounds, images and emergency re-alerts. Communication › Push | Freemium | API key | JSON | 100–1k/day | Live |
ResendSends transactional and marketing emails from your app via a REST API with domain verification. Communication › Email | Freemium | API key | JSON | 100–1k/day | Live |
Retell AIAI voice agents that answer and place phone calls or run in the browser, with call transcripts and analysis. Communication › Voice | Free trial | API key | JSON | — | Live |
Sendbird Chat APIBackend for in-app 1:1 and group chat: users, channels, messages, moderation and translation via a server API. Communication › Chat | Free trial | API key | JSON | — | Untested |
SendGridTransactional and marketing email delivery API with templates, webhooks, and delivery analytics. Communication › Email | Free trial | API key | JSON | — | Untested |
SentSends SMS, WhatsApp and RCS messages through one API with automatic channel routing and fallback. Communication › SMS | Paid | API key | JSON | — | Untested |
SMTPfastSends transactional email and manages contacts, segments and broadcast campaigns via a REST API. Communication › Email | Freemium | API key | JSON | 100–1k/day | Live |
Stream ChatHosted backend for in-app messaging: channels, threads, reactions, typing indicators and moderation. Communication › Chat | Freemium | API key | JSON | — | Untested |
SweegoSend and track transactional email, SMS, and push notifications through one multichannel API. Communication › Email | Freemium | API key | JSON | 100–1k/day | Live |
Telnyx Voice APIMake and control phone calls with text-to-speech, recording, live transcription and audio streaming. Communication › Voice | Paid | API key | JSON | — | Live |
TextbeltSend SMS with one POST, then check delivery status and remaining credit; prepaid packs, no monthly fee. Communication › SMS | Freemium | API key | JSON | <100/day | Live |
VapiHosted voice agents for phone and web calls that combine your choice of speech, LLM and voice providers. Communication › Voice | Free trial | API key | JSON | — | Live |
Xeramail Temp MailCreate disposable inboxes and read incoming mail via API, with auto-extracted OTP codes. Communication › Disposable Email | Paid | API key | JSON | — | Untested |
ZyntraDisposable inboxes for QA/dev testing; create mailboxes and fetch received emails or OTPs by API. Communication › Disposable Email | Freemium | API key | JSON | <100/day | Live |
Atomic MailFreeLive
Self-registers a real email inbox for an AI agent (PoW, no signup) and sends/receives mail via JMAP.
API key · JSON
Unlimited
llms.txt
Best-TempMailFreemiumDown
Creates disposable email inboxes and reads incoming messages, including OTP extraction on paid plans.
None · JSON
1k–10k/day
no machine-readable spec
BrevoFreemiumLive
Send transactional and marketing email, SMS and WhatsApp, and manage contacts via one REST API.
API key · JSON
100–1k/day
llms.txt
dead-dropFreeLive
Create and retrieve end-to-end encrypted, self-expiring text/secret drops without an account.
None · JSON
Unlimited
OpenAPI spec
DropMail.meFreeLive
Create disposable email inboxes via GraphQL, then read or subscribe to incoming mail in real time.
API key · JSON
Unlimited
no machine-readable spec
Email Spam TesterFreeUntested
Sends a test email through 42 deliverability and spam checks, then returns a scored JSON report.
None · JSON
<100/day
llms.txt
EmailJSFreemiumUntested
Sends transactional emails from client-side JavaScript without a backend server.
API key · JSON
<100/day
no machine-readable spec
FreeCustom.EmailFreemiumUntested
Disposable email inboxes with message fetching and automated OTP/verification-code extraction.
API key · JSON
<100/day
llms.txt
Guerrilla MailFreeLive
Generates disposable email addresses and reads their inbox through a simple JSON API, no signup.
None · JSON
Unlimited
no machine-readable spec
httpSMSUntested
Turns your own Android phone into a controllable SMS gateway you call over HTTP.
API key · JSON
—
llms.txt
ImprovMXFreemiumLive
Manages email forwarding aliases and SMTP sending credentials for a custom domain.
API key · JSON
10k+/day
llms.txt
inboxsinkFreemiumLive
Creates disposable inboxes and blocks until a message arrives, extracting OTP codes for test automation.
API key · JSON
<100/day
no machine-readable spec
IndiePitcherFreemiumLive
Sends transactional emails with markdown support and manages contact lists for SaaS apps
API key · JSON
<100/day
OpenAPI spec · llms.txt
mail.tmFreeLive
Creates disposable inboxes and lets apps poll or fetch mail sent to them, no signup needed.
API key · JSON
Unlimited
llms.txt
MailjetFreemiumLive
Transactional and marketing email sending, contact list management, and delivery stats via REST API.
API key · JSON
100–1k/day
no machine-readable spec
MailsacFreemiumLive
Disposable email inboxes for QA/testing: read, search and validate mail via API, webhooks or websocket.
API key · JSON
<100/day
OpenAPI spec
MailtrapFreemiumUntested
Transactional and bulk email sending API with a built-in sandbox for safely testing emails.
API key · JSON
100–1k/day
MCP server · llms.txt
NotilifyPaidLive
Sends transactional SMS (OTPs, alerts) via API with delivery tracking and webhook status updates.
API key · JSON
—
no machine-readable spec
ntfyFreemiumLive
Send push notifications to phones and desktops with a plain HTTP PUT/POST to a topic; no signup needed.
None · JSON
100–1k/day
no machine-readable spec
OneSignalFreemiumUntested
Send push, email, SMS and in-app messages from one REST API, with segmentation and delivery data.
API key · JSON
—
llms.txt
Plivo SMS APIFree trialLive
Send and receive SMS and MMS worldwide, with delivery reports and message logs; per-message US pricing.
API key · JSON
—
no machine-readable spec
PostStackFreemiumLive
EU-hosted transactional and marketing email sending with templates, broadcasts and webhooks.
API key · JSON
100–1k/day
llms.txt
Pusher BeamsFreemiumUntested
Sends push notifications to iOS, Android and web apps via device interests or authenticated users.
API key · JSON
—
no machine-readable spec
Pusher ChannelsFreemiumUntested
Managed realtime pub/sub messaging with presence channels for live dashboards, chat, and activity feeds.
Other · JSON
10k+/day
no machine-readable spec
PushoverFreemiumLive
Send push alerts to iOS, Android and desktop with priorities, sounds, images and emergency re-alerts.
API key · JSON
100–1k/day
no machine-readable spec
ResendFreemiumLive
Sends transactional and marketing emails from your app via a REST API with domain verification.
API key · JSON
100–1k/day
llms.txt
Retell AIFree trialLive
AI voice agents that answer and place phone calls or run in the browser, with call transcripts and analysis.
API key · JSON
—
OpenAPI spec
Sendbird Chat APIFree trialUntested
Backend for in-app 1:1 and group chat: users, channels, messages, moderation and translation via a server API.
API key · JSON
—
no machine-readable spec
SendGridFree trialUntested
Transactional and marketing email delivery API with templates, webhooks, and delivery analytics.
API key · JSON
—
OpenAPI spec
SentPaidUntested
Sends SMS, WhatsApp and RCS messages through one API with automatic channel routing and fallback.
API key · JSON
—
no machine-readable spec
SMTPfastFreemiumLive
Sends transactional email and manages contacts, segments and broadcast campaigns via a REST API.
API key · JSON
100–1k/day
llms.txt
Stream ChatFreemiumUntested
Hosted backend for in-app messaging: channels, threads, reactions, typing indicators and moderation.
API key · JSON
—
no machine-readable spec
SweegoFreemiumLive
Send and track transactional email, SMS, and push notifications through one multichannel API.
API key · JSON
100–1k/day
OpenAPI spec
Telnyx Voice APIPaidLive
Make and control phone calls with text-to-speech, recording, live transcription and audio streaming.
API key · JSON
—
no machine-readable spec
TextbeltFreemiumLive
Send SMS with one POST, then check delivery status and remaining credit; prepaid packs, no monthly fee.
API key · JSON
<100/day
no machine-readable spec
VapiFree trialLive
Hosted voice agents for phone and web calls that combine your choice of speech, LLM and voice providers.
API key · JSON
—
OpenAPI spec
Xeramail Temp MailPaidUntested
Create disposable inboxes and read incoming mail via API, with auto-extracted OTP codes.
API key · JSON
—
no machine-readable spec
ZyntraFreemiumLive
Disposable inboxes for QA/dev testing; create mailboxes and fetch received emails or OTPs by API.
API key · JSON
<100/day
OpenAPI spec
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Choosing a Communication API
Is there a free Communication API?
Yes. Atomic Mail, dead-drop, DropMail.me, Email Spam Tester, Guerrilla Mail and 1 other are free to use, and Resend, OneSignal, Brevo, EmailJS, FreeCustom.Email and 16 others have a free tier alongside paid plans.
Which Communication APIs work without an API key?
dead-drop, Email Spam Tester, Guerrilla Mail and ntfy need no key or sign-up, so you can try them with a plain request.
Can I call a Communication API from front-end JavaScript?
dead-drop, Guerrilla Mail and ntfy allow cross-origin requests and need no key, so they work straight from the browser. For the others, call them from your server so your key stays private.
Can I use Communication APIs in a commercial project?
Resend, SendGrid, OneSignal, Atomic Mail, Brevo and 15 others permit commercial use. mail.tm and Mailsac restrict it, for example to non-commercial or attributed use, so read the terms first.
Which Communication APIs work with AI agents?
Mailtrap has an MCP server, so an AI agent can call it directly. SendGrid, dead-drop, IndiePitcher, Mailsac, Retell AI and 3 others publish an OpenAPI spec for generating clients and tools.
Browse by subcategory: Email APIs · SMS APIs · Push APIs · Chat APIs · Voice APIs · Disposable Email APIs