In the API responses we return links to related endpoints. Some of the targetSchema and schema fields pointed to outdated JSON Schema files. We changed these to reference the equivalent Swagger definition.

In the past, we deprecated our use of JSON Schema in favor of Swagger. Note that although we’re updating some of the link definitions, we don’t advise relying on them — we’d like to investigate deprecating them in the future. Instead, we recommend using the reference documentation or Swagger spec.

We upgraded the underlying hardware of our database service resulting in significant performance improvements.

We were observing performance and occasional stability issues relating to our older database hardware. By doubling processor, memory, and network card speeds as well as tripling disk I/O speeds with newer NVMe solid-state drives, our database service is processing tasks in comfort. In turn, our web application service is processing tasks faster as well.

We fixed a bug in the POST Campaigns endpoint regarding invalid request body parameters for non-rss campaigns.

We were receiving requests that were attempting to create non-rss type campaigns with an rss_opts field. These requests were throwing exceptions and returning 500 status codes to users. We now return a 400 status code if rss_opts are provided for non-rss type campaigns.

We shut down the Mailchimp API Playground. 

The API Playground let users explore the Marketing API and the data it returns. Instead, we recommend users learn about and explore their API data with our new API Reference docs, which include rich code snippets written for our official client libraries.

We fixed a mistake in the query parameters for filtering a list of automations. 

The query parameter filters were incorrectly documented as before_send_time and since_send_time. The correct parameters are before_start_time and since_start_time.

We removed the unused Update Automation endpoint.

This endpoint was limited in which automations workflow types could be updated, and no successful calls had been made to this endpoint in many months. We opted to deprecate it until we can provide a more useful method of updating automations.

Since we don’t see any usage of this endpoint, we don’t expect any action to be needed.

We rewrote large parts of the API internals. There should be little to no external impact on API behavior, besides slight performance fluctuations.

The internals of the API had accumulated a fair bit of kludge over the past 5-10 years, so we rewrote a good portion of them and have identified several discrepancies in behavior across endpoints. During the rewrite, we learned about and ironed out many of the discrepancies that were causing friction internally — and in the process, we identified further changes that we’ll implement in the future to make behaviors across the APIs more consistent.

We made a variety of fixes to our Swagger spec to improve the documentation.

There were endpoints included in the documentation that have no function except to organize the path hierarchy. For example: /reporting. We removed them since they’re not useful on their own. Additionally, there were some body parameters included incorrectly, for properties that are read-only and can’t be passed in as a parameter

We updated our Swagger spec to make it match the spec used in the codegen repo.

We use a Swagger spec to produce API client libraries from the codegen repo. Doing this required tweaking the Swagger spec that’s automatically produced by our internal API definitions, so there was some drift between the spec in the codegen repo and the one we produce automatically. We backported the changes, so our automatically-produced spec matched the one in the codegen repo. Now that this work is done, we can rely on the automatically produced spec for client libraries.

We’ve stopped calculating the (deprecated) existing, options, and imports fields for the Growth History endpoint, and API responses will have a value of zero for these fields.

The data in these fields can be accessed in a more understandable way in other fields, and returning the data in these fields was slow and added infrastructure load when these endpoints were requested.

We have released API client libraries for the Marketing and Transactional APIs, supporting PHP, Node.js, Ruby, and Python.

We wanted to make it easier for developers to integrate their applications with both of our APIs in the language of their choice. The new libraries are generated from publicly available API specs and published on the respective package managers for each supported language.

It was possible to force multiple confirmation emails to be sent to a member when using identical PATCH or PUT requests to the Members resource. We’ve corrected this behavior by preventing the duplicate confirmation emails from being sent.

Before this change, multiple confirmation emails would be sent to a member’s inbox, which could potentially be used for abuse.

The security team has implemented stricter rules around redirect URL matching in our OAuth 2 implementation. We now only support exact matching on the redirect URI to adhere to the OAuth 2 spec.

Before this change, our redirect URL matching didn’t conform to the OAuth 2 spec. Strictly adhering to the spec results in more predictable behavior and fewer surprises.

We changed the behavior of the unsubscribe merge tag to obfuscate the email address of the person who clicked the link. Instead of showing the entire address, the md_email parameter now displays the address as something like x****@x***.*** .

Previously, if a customer clicked an unsubscribe link, their email address was displayed on the Unsubscribe page in full. By obfuscating the email address, this change provides better security.

Previously, if an object was passed as the value of the email field in a POST to the Lists/members endpoint, the server would return a 500 error. Now we return a 400 error with a clear error message.

We saw multiple occurrences of these errors in our logs. Ideally, badly formed requests shouldn’t return 500 errors, and we should give more information to callers when errors do occur.

We’ve updated our Swagger file to make it OAS 2-compliant. Our API Reference documentation is generated from our Swagger file. Before this change, we used a number of non-standard field names to control formatting in those docs. We cleaned those fields up and added testing to prevent drift in the future.

We’d heard from developers that an OAS 2-compliant Swagger would greatly improve the developer experience for the Marketing API. This update makes it possible, for example, to directly use our Swagger file in Postman to more easily make requests to our API endpoints, in addition to better integration with many other OAS-friendly tools.

Previously, null-valued entries in the properties object passed to the Events endpoint would cause a server error, returning a 500 to the client. With this change, we treat null property values as empty strings.

This change gives clients a little more flexibility with how they format the properties parameter, and it cleans up our server logs.