OpenCRM has a pre-built integration with MailChimp that is free to use and set up. 

In order to set up the integration, you will need:

• Admin access or configuration privileges in OpenCRM
• A MailChimp user account (either free or paid-for account)
• Your MailChimp API key (at the time of writing, this article will walk you through retrieving that key)*

To configure your MailChimp integration:

1. Go to Settings > Integrations > Bulk Mail / Campaign Management
2. You should see this configuration screen (or something similar):
   
   
3. Type your API Key in the space provided  (at the time of writing, this article will walk you through retrieving that key)*
4. Tick the Enabled box
5. Click Save

Setting up a Campaign

1. Go to your Campaign module in OpenCRM and click New Campaign
2. Fill in the Campaign Information and Description fields
   
3. Then add your MailChimp information, be sure to fill in the following fields that are required by MailChimp:

If you choose to put a URL in the "Content URL" field, MailChimp will use this as the content of the e-mail instead of whatever template is chosen.

4. The dropdown lists for your MailChimp Audience and Folder should be populated automatically.**
5. Click Save
   This will save the information in OpenCRM, it will not sync with MailChimp.
6. When you are ready to sync with MailChimp, open the Campaign in consult and click "Sync with MailChimp."
   
   This does not send the email. When you click the button several things will happen to ensure your Campaign is fully integrated with MailChimp:

7. To send your Campaign Email, simply navigate over to MailChimp and send it from there. All campaign statistics will be reflected in OpenCRM (30min sync cycle) until you close the Campaign.

What is the Campaign Mail To Name?

(taken from the following Mailchimp FAQ: http://kb.mailchimp.com/campaigns/design/set-up-or-change-email-subject-from-name-and-from-email-address-on-a-campaign)

Personalize the "To:" field

When you send an email campaign to someone, you should address it to their name, if you have it in your database, instead of just their email address. Spam filters are less likely to block you if you know the recipient's name. Use the MailChimp merge tags to auto-populate the "To:" field with your subscribers first names.

If you don't have name information for all of the recipients on your list, MailChimp recommend that you don't personalize this field or that you set up a default value that will display in place of missing information. Some email programs are unable to render your campaign properly if there isn't a value in the To: field.

Please refer to the MailChimp help section for more information (see link above).

How are Unsubscribes managed?

•    If a Contact unsubscribes in MailChimp, their record in MailChimp will be marked as such. The "unsubscribe" statistic will feed back into OpenCRM and will be visible on the Campaign itself as a number. Note that OpenCRM will not show you who has unsubscribed.

•    On subsequent syncs to MailChimp, anyone who has previously unsubscribed in MailChimp will NOT get re-added to an Audience, as their record has been flagged in MailChimp.

•    If a contact is marked as Do Not Email in OpenCRM, if they are included on a campaign that is synced to MailChimp, they will not get sent the email.

"Sync Unsubscribed Contacts to MailChimp"

This additional setting is OFF by default. 

When syncing contacts marked as "Do Not Email" in OpenCRM if this setting is enabled, the contacts subscription status is set to "Unsubscribed" in MailChimp. When syncing contacts NOT marked as "Do Not Email", their subscription status is set to "Subscribed" in MailChimp.

MailChimp Campaign Statistics

* MailChimp FAQ:

Please note that the content of the article cannot be guaranteed to be available by OpenCRM, neither can the content therein.  OpenCRM accepts no responsibility for the external page or its contents.

**How Are Dropdown Lists Populated?

Within the MailChimp Information block within OpenCRM, there are a number of dropdown pick lists: MailChimp Audience, MailChimp Folder, and MailChimp Template.

These fields are populated from MailChimp at a regular interval by OpenCRM.  This interval is 30 minutes.  That is to say that every 30 minutes OpenCRM will sync the lists here with the lists in MailChimp.  If a new list entry is created in MailChimp, the corresponding list in OpenCRM will be updated.

In the case of the templates, this will use any user created templates, as well as the MailChimp “basic” templates.  It does not list all of the MailChimp “gallery” templates as the list would show over 500 templates by default and become unusable.

This sync might not fall on the clock-face 30 minutes, but rather will depend on when the feature was added to a system, and run each 30 minutes from that point.