Using the Mail Chimp API to target the right customers

MailChimp Integration

I would never think of building a tire to use on my car, I’d buy one that is refined, tested and works! So why do so many developers insist in re-inventing the wheel?

I was talking to a Developer recently who wanted to build a mass emailing system to add value to their CRM product. Rather than building from scratch and having to become an expert in the world of email marketing, tracking, spam, and the best practices in that area I suggested looking at integrating a 3rd party email marketing software.

The benefit of taking something that is already refined and feature rich is a quicker time to market, less to develop and maintain (and is improved constantly for you). Additionally, you can often find nuggets that are worth drawing back into your existing systems to improve additional functionality – such as the Member Rating from MailChimp.

What is MailChimp?

MailChimp is a market leading mass mail system and is what I use for my personal blog e-mail list  (just scroll down its on the right if you want to sign up 🙂 – MailChimp’s free plan gives a generous 2000 registered user which is ideal for many small businesses / start ups etc to start benefiting from. They also offer services for nurture campaigns etc which are hugely beneficial in turning prospects into customers.

MailChimp Member Rating

MailChimp is organised by lists, and each subscriber to that list is a member of that list. The MailChimp Member Rating is a star value (1 to 5) that is calculated based on a members engagement with your email blasts for that list.

The MailChimp Member Rating is highly useful to prioritise who to contact first, who are your most engaged subscribers/customers that are likely to respond positively. While it is clearly visible in the online portal as a star rating. (see image) it would be great to have that inside your own software; which brings me back to the huge value I want to immediately get pulled into my application.

MailChimp Stars
MailChimp Star Rating as seen online via the mailchimp portal

MailChimp API and getting the MailChimp Member Rating

Now on its 3rd iteration, the MailChimp API is JSON based and is self documenting (to a point) as the JSON data packets returned have a links section built in describing the paths available to drill deeper into the data (including JSON Schemas on the returned data). In addition the MailChimp documentation online is pretty good, describing how you can define data packet fields, number of records returned and filter based on search criteria.

The MailChimp API is generally based on REST standards, the MailChimp API is broken up into a number of logical sections allowing you to discover

  • Authorised Applications
  • Automations (part of their paid service)
  • Batch Operations
  • Campaign Folders
  • Email Campaigns
  • Conversations from emails sent
  • File Management (of images used)
  • Lists; that your subscribers belong to
  • Reports on Campaigns
  • Email Templates

Calling the MailChimp API and Lists

The MailChimp Member Rating is part of the Lists section. To get the rating for a member you need to first

  • Get a list of the lists
  • Choose the relevant lists
  • Query the list for the member and retrieve their rating from the data returned.

You can also return the entire list of members using a search (I would recommend breaking this into pages based on the data returned with the list (including size) that you fetch in multiple threads simultaneously – but that is for a later post if I get time)

Calling MailChimp API v3 with Delphi

I covered in an earlier post linking to Azure using the REST components in Delphi. While Azure uses XML data packets in the response, MailChimp uses JSON which makes it a lot simpler to integrate quickly. In the rest of this post I will cover what I needed to do to Integrate with the Mail Chimp API.

Step 1 – Authentication

There are 2 authentication methods for the API: HTTP Basic authentication and OAuth2. The easiest way to authenticate is using HTTP Basic authentication. Mail Chimp takes any string as your username and your API Key as the password (you create the MailChimp API Key from your MailChimp account)

Delpjhi THTTPBasicAuthenticator Component
Delphi THTTPBasicAuthenticator Component

Step 2 – Setup Base URL

With the THTTPBasicAuthenticator setup, you are ready to add the TRESTClient component.  The TRESTClient allows you to easily manage the location of the API that you are calling and makes it easy to switch between servers for testing and live or for different clients. In this case we are just calling the live data.

Set the

  • BaseURL – https://<dc>
    • Note: replace <dc> with the server your account is linked to – you can see this when you log in to your MailChimp account. My account was on Server us11
  • Connect the Authenticator to manage the authorisation headers/handshake.

    TRestClient Delphi MailChimp
    TRESTClient being used with Delphi for MailChimp

Step 3 – Getting a list of list from your MailChimp account

Lists exist under the verb “lists” – To get the lists you need to call the API BaseURL + “/lists” e.g.


The lists verb is added to a TRESTRequest component, which is linked to the TRESTClient. You also will need a TRESTResponse to collect the output from the RESTRequest. Lets start with just getting the raw JSON results and then look at how to work with it.

The image below shows the components added and the properties you nee to check are set on the RESTRequest.

Fetching the list of Lists from MailChimp TRESTRequest and TRESTResponse
Fetching the list of Lists from MailChimp TRESTRequest and TRESTResponse

At this point. You have the URL and authentication setup and somewhere to put the resulting data packet. You should be able to right click on the RESTRequest and Execute, (YES AT DESIGN TIME)

RESTRequest Execute

Resulting in a 200 result.

RESTReqiuest Result OK

The Delphi REST Components have now fetched the data packet using the authentication provided, and you can now see that the data by checking the Content property of the RESTResponse.

RESTResponse result JSON data packet
RESTResponse result JSON data packet (parts greyed out for privacy reasons)

WOW that was easy! No code written yet and data being fetched! Now to get the actual list.

To access an individual list, a GET request is required. This is a slight de-normalisation of REST standards, as a parameter is used like a VERB, however it makes sense for the readability of the URL and the way it drills down so lets roll with it.


Getting the ListID from the JSON data packet

The first step to calling the list specific API call is to get the ListID. To extract the ListID out of the data packet fetched, you need to parse the JSON, but how best to do that? Lets explore two different options depending on your preference.

Option 1) Like TDataSet? Is the data in a JSON Array?

Using TDataSet is great, as it provides a quick easy way to SaveToFile / LoadFromFile or linked into a local database allowing caching of data with little work.

If the data packet returns a JSON array, you can convert this array into a TDataSet using the TRESTResponseDataSetAdapter. Linking the RESTResponse and a TDataSet, the resulting RESTRequest will automatically populate the DataSet with the node specified in the RootElement when it returns.

JSON to TDataSet MailChimp Lists
Setting up RESTResponseDataSetAdapter to read in the “lists” array from the data packet

Converting to a TDataSet, you can then work with the result like any other TDataSet. (e.g. Bind it to a Grid) and get the value by referencing the TField.

List Of Mail Chimp Lists
Example of TDataSet output using mailchimp list API
Option 2) Would you rather work with a Classes and Object representations of your JSON?

I posted on how to build a Delphi Object from JSON using JsonToDelphiClass, a tool I stumbled across while researching the MailChimp API. (see video below for demo)

Using JsonToDelphiClass you can create a Delphi class based on an actual JSON data packet. Using the steps above, the JSON data is easily accessible to copy from the TRESTResponse.Content property ready to paste into JsonToDelphiClass to create the Delphi unit.

While the tool does a good job at creating something that will work, its definitely worth checking the created class against the JSON schema for the data packet in case of missing properties.

JsonToDelphiClass – Click for full image

The default is to have a unit called RootUnit and TRootClass. You can modify those defaults in the JsonToDelphiClass UI or use refactoring afterwards. Either way you now have classes that can be used to make objects to work with at run time.

Click for my earlier post on using TJson.JsonToObject.

Date Times from JSON in Delphi

Note: While the generated unit works out the box, I added [joIgnoreEmptyStrings, joDateFormatISO8601] to the TJsonToObject calls as I updated some of the object properties to be TDateTime rather than strings. This resulted in TDateTime rather than strings for date and time values.


Using the Generated Delphi Class based on JSON

Using the new unit, just add it to your project and to your uses clause and then you can covert the JSON to Objects at runtime with code similar to this… (note – I change TRootClass to TMCLists)

procedure TForm2.Button2Click(Sender: TObject);
  RC: MailChimpLists.TMCLists;
  RC := TMCLists.FromJsonString(RESTResponse1.JSONText);

Step 4 – Details on a MailChimp List Member

Now you have a list of the MailChimp lists on the account, its possible to check each one based on the list ID for the members email address.

The email address is passed as a parameter, called the subscriber hash, and is made by using a MD5 hash of the lowercased email address.


The introduction of System.Hash in RAD Studio XE8 makes the use of MD5 really easy.  e.g. to convert an email into a hashed string you could do something like

uses System.Hash;


hash := THashMD5.GetHashString('');

In a similar way to selecting the lists before hand it is possible to add in a new RESTRequest, connected to the RESTClient and a RESTResponse, connected to the RESTRequest.

Setting the RESTRequest Resource property will automatically create parameters, as named inside the curly brackets.

TRESTRequest URL Segment Paramaters
TRESTRequest URL Segment Paramaters

Using the steps described above, it is now just a case of repeating the process, making sure the parameters are defined (select on in the dialog window to enter the value). The member Rating is on the returned data so will be a property of the new generated class.

If you want to fetch the JSON without having to use the components,  you can use the REST Debugger.

Getting the Member Rating from the JSON

Rather than writing out the same steps again, I’ve covered the steps using JsonToDelphiClass and the REST Debugger in the following video. Which includes how to set the parameters on the REST Debugger.

4 thoughts on “Using the Mail Chimp API to target the right customers”

  1. Hi Stephen,

    I got it working, however, do you have any example on how to create a new mailchimp list, using the rmPost-method (Rest)?

    I can’t seem to get that working?

    kind regards,

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