This extension helps you keep a CiviCRM group in sync with subscribers of a Mailchimp list. It can sync different CiviCRM groups to different Mailchimp lists.

Additionally, if you use Mailchimp's Interests feature, you can map particular Mailchimp interests to a CiviCRM group. You can choose whether this is a group that the subscriber can edit (using Mailchimp's forms), or not.

Some updates happen in near-real time. So once set-up, if someone new subscribes using a Mailchimp embedded sign-up form, they will be added to CiviCRM (if not already found) and joined to the appropriate group. Likewise, if you use the "Add to Group" widget on a contact's Groups tab to add someone to a group that is sync-ed with a Mailchimp List, they will be immediately added. Likewise with individual unsubscribes/removals.

However not all updates are possible (or desireable) this way, and to cope with these there's two mechanisms offered:

1. Pull Sync: updates CiviCRM from Mailchimp, assuming Mailchimp is correct. You'd do this if you had just made a bulk change at Mailchimp, e.g. you'd just imported a new list of contacts to a list and you wanted to make sure that these contacts were in CiviCRM.

2. Push Sync: updates Mailchimp from CiviCRM, assuming CiviCRM is correct. You'd do this if you'd just made a bulk change at CiviCRM, e.g. added/removed a load of contacts to one or more sync-ed groups, or changed records such that now they qualify (or cease to qualify) for membership of a Smart Group.

Typically day-to-day changes made at Mailchimp (poeple clicking unsubscribe, or individuals subscribing or updating their preferences) are all done right away, so except for bulk changes that you do to your list deliberately, you usually do not need to use the Pull.

You can set up the Push to run at scheduled intervals, if you find that's useful, otherwise do it after a change, or at least before you send out an email.

Note: syncing works best when done regularly. If changes are made at both ends there's no way to figure out which way is correct and you'll be forced to choose: pull or push? So it's important you have an awareness of this in your day-to-day workflows.

Until you're confident in the way this works and your own workflows, make sure to backup both your mailchimp and civicrm contacts. Regular periodic backups are also sensible practise.

1. Download extension from https://github.com/veda-consulting/uk.co.vedaconsulting.mailchimp/releases/latest.
2. Unzip / untar the package and place it in your configured extensions directory.
3. When you reload the Manage Extensions page the new “Mailchimp” extension should be listed with an Install link.
4. Proceed with install.

Before the extension can be used you must set up your API keys. To get your Mailchimp account's API you should follow Mailchimp's instructions.

Once you’ve setup your Mailchimp API key it can be added to CiviCRM through "Mailings >> Mailchimp Settings" screen, with url https://<<your_site>>/civicrm/mailchimp/settings?reset=1. Using “Save & Test” button will test that a connection can be made to your Mailchimp account, and if your API settings are correct.

In Mailchimp: Set up an empty list, lets call it Newsletter.

In CiviCRM: you need a group to track subscribers to your Mailchimp Newsletter List. You can create a new blank group, or choose an existing group (or smart group). The CiviCRM Group's settings page has an additional fieldset called Mailchimp.

Choose the integration option, called "Membership Sync: Contacts in this group should be subscribed to a Mailchimp List" then choose your list name.

Ensure the tickbox is ticked that says "Ensure lists's webhook settings are correct".

Save your group's settings.

The next step is to get CiviCRM and Mailchimp in sync. Which way you do this is important. In our example we have assumed a new, blank Mailchimp list and a populated CiviCRM Group. So we want to do a Push CiviCRM to Mailchimp Sync. However, if we had set up an empty group in CiviCRM for a pre-existing Mailchimp list, we would want to do a Pull Mailchimp to CiviCRM sync. If you get it wrong you'll end up removing/unsubscribing everyone!

So for our example, with an empty Mailchimp list and a CiviCRM newsletter group with contacts in, you'll find the CiviCRM to Mailchimp Sync function in the Mailings menu.

You'll notice a tick-box for Dry-Run. If this is ticked then all the work is done except for the actual updates. Use this if you're at all unclear on what's about to happen and check the results make sense.

Push the Sync button and after a while (for a large list/group) you should see a summary screen.

Any un/subscribes from the Mailchimp end will be handled (almost) instantly using the webhook. Changes at the CiviCRM end will also be handled (almost) instantly using CiviCRM database post hook.

Note: If anybody is added/removed to group in civiCRM, they get subscribed/unsubscribed to Mailchimp immediately. If Webhook is set properly in Mailchimp, then subscribe/unsubscribe in Mailchimp is treated back to civiCRM immediately as addition/deletion to group

We have an upcoming feature that will give you the option to force a CiviCRM to Mailchimp sync which will automatically do the necessary deletions, but this is not included in the current version. Watch this space.

For this example we'll set up two interest groupings in Mailchimp, one called Things I like that is publically viewable, and one called Private that is hidden from subscribers. Within "Things I like" add Mailchimp Groups such as "bananas", "organic farming", "climate change activism". Within the "Private" Mailchimp Interest Grouping, you might add Mailchimp Groups called "major donor", "VIPs" etc.

Please take care and follow Mailchimp's help pages for how to restrict the visibility of the Private interest grouping.

Now back in CiviCRM, setup groups to map to these Mailchimp Groups. When you look at the CiviCRM group's settings page, choose "Interest Sync: Contacts in this group should have an "interest" set at Mailchimp".

Here you can see the two options about whether Mailchimp subscribers are supposed to be able to edit their membership of this interest grouping.

So for the Private interest grouping, choose the first, No option, for the public "Things I like" one, choose the second option.

Please note that while it's possible to configure one Mailchimp Group to be updatable and another to be non-updatable within the same mailchimp interest grouping, this will lead to unpredictable results. Stick to the rule: if it's public, it should be updateable, if it's hidden/private, it should be not updatable.

When you run the sync, these grouping will be updated accordingly. So again, when you first set it up, which source has the data: Mailchimp or CiviCRM? Choose Pull or Push accordingly.

The extension tries hard to match contact details from Mailchimp with existing contacts in CiviCRM. This is explained in the README-tech file and documented in more detail in the code comments including tests.

The basics are:

1. Emails are the primary thing to match (obviously!). While CiviCRM will always choose a "bulk mail" email address for giving to Mailchimp, it will check every email, bulk mail or other when trying to find a contact.

2. The default Mailchimp FNAME and LNAME "merge fields" are assumed and are an important part of a successful sync workflow. There is the option to use a NAME merge field at Mailchimp, but this is far less helpful in many ways, so avoid this if you can.

3. Precidence will be given to contacts that are in the sync-ed membership group. So if the same email and name belongs to two contacts but one is in the membership group, it will assume that's the one to work with.

4. If there are multiple contacts with the same name and email, and none are in the group, a random one will be picked. Then after this will be preferred (see point 3).

5. "Titanics" There are still cases of messy data in CiviCRM that cannot be resolved. e.g. 2 contacts have the same email, neither is in the group, and neither has a name that matches the incoming data from Mailchimp. These are considered un-sync-able. It would be wrong to create another contact (possibiliy of adding to the duplicates) and we can't choose between them. Such contacts are excluded from the Sync and will remain as they are on Mailchimp, until such time that the duplication or incorrect names in CiviCRM is sorted out. These contacts are listed on the summary page after a sync operation.

When Mailchimp determines an email must be 'cleaned' CiviCRM will put that email "on hold". Cleaned in Mailchimp parlance means the email is duff, e.g. hard bounces.

Mailchimp have certain policies in place to protect their own interests and sender reputation. These can cause problems with sync.

For instance if someone unsubscribes from a list using the link at the bottom of their email, you are not allowed to re-subscribe them. Previously there have been work-arounds to this (e.g. delete the member and re-add them) and while there are still loopholes in Mailchimp's API that could be exploited to this end, as it is against their policy we should not design a system that makes use of these since the loopholes (bugs) could be fixed at any time, breaking our system without notice.

Note that this rule does not apply if it was us (CiviCRM) who unsubscribed the member.

Likewise you cannot (or are not supposed to be able to) re-subscribe a 'cleaned' email address.

Mailchimp's policy is that these emails can only be updated to "pending" by the API, which means Mailchimp sends a "do you want to subscribe to..." email. The extension does not currently handle this case.

Originally work was done by the science gallery, then Veda Consulting and Artful Robot. Thanks also to Sumatran Orangutan Society for funding some of the work to implement Mailchimp API v3.

Please see <README-tech.md>