ZeroSettle vs Sendblue: price, outbound limits and fallback (2026)

How we compared ZeroSettle and Sendblue

We compared ZeroSettle and Sendblue on nine criteria, fixed before writing the results. Both are managed iMessage APIs (see what an iMessage API is). ZeroSettle is an iMessage API: a real phone number on real iMessage, running on Apple hardware we operate for you, that your code texts customers from and hears back on through a bearer token and signed webhooks.

• Price of a number that can message first
• Outbound limits
• Android reach
• Webhook security
• Hosted or bring-your-own AI
• SOC 2 and HIPAA
• Features: groups, calling, porting, SDKs, CRMs, read status
• Trial, refund and number replacement
• Published track record

ZeroSettle vs Sendblue at a glance

Sendblue covers more channels, features and compliance paperwork. ZeroSettle publishes a price for a number that messages first ($49 a month, where Sendblue's outbound plan is priced on request), signs its webhooks and hosts an AI agent (Beta).

How do ZeroSettle and Sendblue prices compare?

ZeroSettle's cheapest number that can message people first costs $49 a month (Pro). Sendblue's cheapest dedicated line costs $100 a month and is inbound-first; Sendblue's plan with full outbound messaging, Enterprise, has no published price.

Neither vendor charges per API message: Sendblue lists $0 per-message, A2P, carrier-surcharge and SMS-fallback fees. ZeroSettle meters only the hosted agent's texts, one AI credit each, with packs of 1,000 for $50 or 5,000 for $200. ZeroSettle numbers can sell out, with a waitlist. See ZeroSettle's plans and iMessage API pricing compared.

Who can start conversations, and how many?

Both ZeroSettle plans can message people first, and anyone who texts a ZeroSettle line first is never limited. On Sendblue's AI Agent plan, people who text first count toward a daily limit and re-opening a quiet conversation has its own cap. Sendblue's limits page sets messaging-first limits for “Blue Ocean” plans, which its pricing page doesn't list.

ZeroSettle's day also runs 3 AM to 3 AM Eastern.

One day on one number

Say 40 people text in from an ad, 15 of last week's leads get a check-in, and 5 people who requested a quote on a web form get a first text.

• ZeroSettle Pro ($49): the 40 and the 15 never count toward new contacts (each check-in still waits for a reply after 2 unanswered texts). The 5 form leads use all 5 of the day's new contacts; more would need Growth.
• Sendblue AI Agent ($100): the 40 count toward 1,000 inbound contacts and the 15 toward the 200 follow-up limit. The 5 form leads need messaging first, which Sendblue's pricing page puts under Enterprise.
• Sendblue under Blue Ocean limits: the 5 fit, and Sendblue's pre-reply rules allow no link and at most 300 characters in each first text.

A first text that asks for a reply works under both rule sets:

How do ZeroSettle and Sendblue webhooks and security differ?

ZeroSettle signs every webhook with HMAC-SHA256 over a timestamp and the raw body. Sendblue's webhook docs describe a secret you set, per webhook or as one globalSecret, which Sendblue includes in the request headers; they describe no signature over the payload.

A secret in a header travels with every request, so anyone who sees one request (in a log or a proxy) can send forged ones, and nothing ties it to the body or to a time. ZeroSettle's secret is never sent with a webhook: the X-ZeroSettle-Signature header covers the exact body, so a changed body fails the check, and its timestamp lets you reject a request more than 300 seconds old, so a captured one can't be replayed later. ZeroSettle's signing secret is shown once and rotates when you re-register the webhook. The check, from ZeroSettle's webhook docs:

import hmac, hashlib, os, time

SECRET = os.environ["ZEROSETTLE_WEBHOOK_SECRET"]

def verify(header: str, raw_body: bytes, tolerance: int = 300) -> bool:
    # header: X-ZeroSettle-Signature: t=<unix>,v1=<hex>
    try:
        parts = dict(p.split("=", 1) for p in header.split(","))
        t, v1 = int(parts["t"]), parts["v1"]
    except Exception:
        return False
    if abs(time.time() - t) > tolerance:
        return False
    expected = hmac.new(SECRET.encode(), f"{t}.".encode() + raw_body, hashlib.sha256).hexdigest()
    return hmac.compare_digest(expected, v1)

SOC 2 and HIPAA

Sendblue says it is “SOC 2 Type II certified with HIPAA support”, offers its Type 2 report on request, and requires “our dedicated HIPAA instance” for HIPAA. ZeroSettle claims neither: its homepage lists “SOC 2, DPA and security reviews” only in the custom-priced Enterprise plan, and its terms prohibit protected health information without a Business Associate Agreement with ZeroSettle. Whether HIPAA applies to your messages depends on who you are and what you send; this isn't legal advice, so check with counsel. See how ZeroSettle secures tokens, webhooks and data.

When ZeroSettle is not a fit: choose Sendblue

Sendblue is the better choice when you need reach, paperwork or features ZeroSettle lacks today.

• You must reach Android users or anyone not on iMessage. Sendblue falls back to RCS, then SMS. ZeroSettle's docs say “The address must be on someone's iMessage; there is no SMS or email fallback.”
• You need a SOC 2 Type II report or HIPAA coverage now. Sendblue lists “SOC 2 & HIPAA” on its Enterprise plan, offers its audit report on request and runs HIPAA customers on a dedicated instance; ZeroSettle claims neither.
• You need group chats, FaceTime Audio calls, vCards, or video and other files. Sendblue's groups are in beta on select plans, and its homepage FAQ says it supports voice memos and other file types such as mp3 and mp4. ZeroSettle conversations are one-to-one, and its attachments are photos and voice messages only.
• You want to keep your current number. Sendblue ports numbers; ZeroSettle numbers remain ZeroSettle's property.
• You want read status, official SDKs or native CRM integrations. Sendblue reports delivered and read status by webhook, ships Node.js and Python SDKs, and connects natively to CRMs such as Salesforce and HubSpot. ZeroSettle reports only message.sent and message.failed, has no SDK (it is plain HTTPS and JSON), and today connects natively only to Close, with Salesforce listed as coming soon; for other tools you build on its webhooks.
• You want to test for free first. Sendblue's sandbox costs nothing; ZeroSettle has a 30-day money-back guarantee instead of a trial.
• You want a longer public track record. Sendblue says it has “Five years in production”; ZeroSettle publishes no comparable figure.

When ZeroSettle is the better choice

ZeroSettle is the better choice when one number must start conversations at a published price, or the AI should run without your server.

• A listed price for messaging first: Pro, $49 a month for 5 new contacts a day plus unlimited messages with people who message you first; Growth, from $599/mo, adds numbers that work as one.
• A hosted AI agent: on a number set to “Managed by AI Agent” (Beta), ZeroSettle's hosted agent answers every inbound text from the business context you write, with no server of yours involved, and uses one AI credit per text it sends. Sendblue's AI Agent plan carries messages for a model you run. See how the hosted agent works.
• Text-first contacts never count toward the new-contact limit, nor do ongoing conversations.
• Signed webhooks, and a published replacement policy for a flagged number (see the FAQ).
• Also documented: a live event stream, a Sign in with iMessage recipe, and an MCP connector that signs you up, mints your API key and tests your webhook.

Both offer typing indicators, tapbacks, photos and voice messages, a shared name and photo, an MCP server, STOP handling and a Close integration, so those decide nothing. To try ZeroSettle, get a Pro number or read the API docs.

How we checked

Every Sendblue fact comes from Sendblue's own public pages as of October 8, 2026 and listed under Sources. We did not test paid accounts. ZeroSettle facts come from its API docs, homepage and terms. Claims we could not verify were left out, and Sendblue's comparison pages were not used for Sendblue facts. We re-check this page quarterly and log changes below. For other vendors, see ZeroSettle vs Linq, 14 iMessage API providers compared and the comparisons hub.