Sendloop API + MCP (2026): v3 from 2011, no official MCP server

Sendloop still advertises a “full-featured API and webhooks”, but the API you would build against is v3, announced on September 28, 2011, and no v4 has ever followed. All three official client libraries are PHP, all have been renamed “legacy” by Octeth, and the newest release among them shipped on April 1, 2015. There is no official MCP server, no public endpoint catalogue, no OpenAPI spec and no published rate limits, and the documentation URL Sendloop’s own SDK points to returns HTTP 404.

Integrating in 2026 is therefore a reverse-engineering exercise supported by one attested command name and three third-party agent wrappers. This page records what first-party sources verify and marks the rest unpublished. For a documented API with maintained SDKs, compare EmailOctopus, MailerLite, Sender and Moosend.

At a glance

MCP integration in 2026

Model Context Protocol is how an AI agent discovers and calls a vendor’s tools without bespoke glue. By 2026 most active ESPs ship a first-party MCP server. Sendloop ships none, so the question is not whether an agent can reach it, it can, through resellers, but how much those resellers expose.

Available MCP servers

All three are third-party, not Octeth, and each needs your own Sendloop API3 key. None is a managed app, so credential handling is yours.

Sendloop API essentials

API v3 is RPC-style, not REST: you POST a form-encoded payload carrying a Command in Resource.Action form, an API key and a response format, and receive JSON back. There are no verbs beyond POST, and status semantics live in the body, not the status line.

The account-scoped design matters more than it looks. Because the PHP SDK takes your subdomain as a separate argument, the request host differs per customer and no single base URL exists to publish. You cannot copy a working call from another account, nor lift one from documentation. Treat the endpoint as configuration from your own account or a support ticket.

Authentication methods

API key, the only documented path

Sendloop authenticates with a per-account key its SDK labels the API3 key, generated at Settings › API Settings. It travels in the request payload, not an Authorization header, consistent with the API’s 2011 design. So the key lands in POST bodies, and there is no documented rotation, scoping or expiry. Treat it as a full-privilege account credential. The account subdomain is a second required argument, the wrapper takes it as its second constructor parameter, and a mismatch surfaces as an authentication error rather than a routing error, which is hard to debug with no documentation.

OAuth 2.0, advertised by a reseller only

Composio’s toolkit lists both OAuth2 and API-key schemes. Sendloop publishes no OAuth documentation, no authorization URL, token endpoint, scope list or client registration. Only the API-key path is attestable, so build against that and treat any OAuth affordance in a third-party console as undocumented behaviour.

Rate limits

Sendloop publishes no rate limit of any kind. Every row below reads unpublished because no official page carries a figure and the help portal that would have held them is offline. These cells are empty by choice, not estimated.

The workaround is empirical: instrument the client, start conservative, back off on anything that is not a clean success. Sane defaults for an undocumented 2011-era API are 1 request per second with exponential backoff and full jitter, a client-side timeout of 30 seconds, and a circuit breaker after 5 consecutive failures. Log every non-success body verbatim, with no error catalogue, your logs are the reference.

Official SDKs

Sendloop has shipped exactly three official client libraries and every one is PHP. All three repositories were renamed by Octeth to carry the word “legacy”, with last commits between 2013 and 2017. There is no official Python, Node.js, Ruby, Go, Java or .NET client.

The first is the general v3 wrapper: Packagist shows v3.0.0 dated April 1, 2015, roughly 6,830 installs, 1 dependent and a “not auto-updated” flag. The second is the MTA transactional client; despite the name it is an HTTP wrapper, not an SMTP client, with no relay credentials, last commit November 16, 2017. The third is a 2013 grab-bag with no install path.

Notable community SDKs

There are none worth naming. Unlike EmailOctopus or MailerLite, Sendloop’s API has produced no maintained third-party client on npm, PyPI or RubyGems. What exists is platform-level coverage: Composio wraps 5 read operations as agent tools, and the official Zapier app handles subscriber CRUD without code. For most teams that beats writing a client against an undocumented API.

Endpoints reference

The caveat first: only one Sendloop command name is attested verbatim in official material, List.GetList, the worked example in the PHP SDK README. Every other row describes a capability a first-party surface demonstrably performs, the MTA SDK, the official Zapier app, Composio’s toolkit, but whose command string Sendloop has never published. Those paths read “unpublished” on purpose; they are not callable strings.

The nearest official reference is the SDK repository; the documentation URL it cites returns HTTP 404.

Read that as a capability inventory, not a call reference. Turning any of it into working code means the legacy PHP SDK or a support ticket.

Code examples

PHP, the only official example

The single published Sendloop code sample in existence. Note the three constructor arguments: key, subdomain, response format.

// Verbatim from the official SDK README
// (github.com/octeth/sendloop-legacy-php-api-wrapper):

$sendloop = new Sendloop\SendloopAPI3('YOUR_API3_KEY', 'SENDLOOP_SUBDOMAIN', 'json');
$sendloop->run('List.GetList', array());
print_r($sendloop->Result);

Python, hand-rolled client

No official Python or Node SDK exists, so this is a minimal RPC helper. The endpoint comes from the environment because no public base URL exists.

# No official Python SDK and no public API reference exist.
# Attested shape: API v3, RPC-style with dotted command names such as
# "List.GetList", an "API3 key" from Settings > API Settings, scoped
# to your account subdomain. The request PATH is not published.

import os
import requests

API_KEY = os.environ["SENDLOOP_API_KEY"]        # from Settings > API Settings
ENDPOINT = os.environ["SENDLOOP_API_ENDPOINT"]  # account-specific, undocumented


def sendloop(command, **params):
    """Call an API v3 RPC command, e.g. sendloop('List.GetList')."""
    payload = {"Command": command, "APIKey": API_KEY,
               "ResponseFormat": "json", **params}
    response = requests.post(ENDPOINT, data=payload, timeout=30)
    response.raise_for_status()
    return response.json()


print(sendloop("List.GetList"))

PHP, transactional send via the MTA SDK

A separate abandoned package. An HTTP wrapper, not an SMTP client; it supports merge variables, custom arguments and tracking flags for opens, clicks, eCommerce and tags.

// Sendloop MTA PHP SDK, last commit 2017-11-16.
// HTTP API client, NOT an SMTP client.

$mailer  = new \Sendloop\MTA\Mailer("YOUR-API-KEY-HERE");
$message = new \Sendloop\MTA\Message();

$message->setFrom("sender@example.com", "Example Sender");
$message->setSubject("Your receipt");
$messageStatusID = $mailer->send("test@recipient.com", $message);
$status = $mailer->status($messageStatusID);

Common gotchas

Deprecations and changelog

Sendloop maintains no changelog and no release-notes page. There is no /changelog path in its sitemap and no status page-status.sendloop.com resolves through the same wildcard and serves the login screen. The timeline below is reconstructed from dated blog posts, Packagist metadata and GitHub timestamps. Every entry predates 2024.

• September 28, 2011-API v3 announced by co-founder Cem Hurturk, with a PHP wrapper then hosted on Google Code. Still current 15 years later.
• April 1, 2015-final release of the official PHP SDK, sendloop/sendloop v3.0.0, on Packagist (about 6,830 installs). Nothing has followed.
• December 9, 2016-“Introducing the new Transaction Email Gateway”, the only official statement that Sendloop offers SMTP access alongside API access. Its documentation is now unreachable.
• November 16, 2017-last commit to the MTA PHP SDK, the transactional client, since renamed sendloop-legacy-mta-api-php.
• May 26, 2023-last content ever published on the Sendloop blog: four posts in one day, including the SPF and DKIM guide, now the most useful surviving Sendloop documentation.

With no vendor changelog, the closest thing to a release feed is the Octeth GitHub organisation. Watch it for the pattern: every actively-updated repository there belongs to the self-hosted Octeth Email Platform, not to Sendloop.

Frequently asked questions