You can send a basic message through the People interface by connecting MailChimp to your account. Once connected, sync your list to MailChimp to use their campaign building tools.
Sync your list in People to a segment in your MailChimp list by selecting Sync Now.
If your account has not yet been connected to your MailChimp account, the Sync Now button will not be available. An Organization Administrator can connect your MailChimp account from the Integrations tab on Accounts.
Once your the sync process has been completed, the sync button will say View in MailChimp. Select that to view your segment in MailChimp.
Check the box to Re-sync every night in case you have others subscribe to the segment and are willing to pay MailChimp for the additional subscribers.
To send an email to the people in your list, select Send Email from the Actions dropdown.
Only Managers and those who have Can email lists permissions will see the option to email people on lists.
Enter your message and choose Send Email to send it to those in your list.
The email will take on the template you've added in MailChimp, adding the body and subject line in their appropriate places.
The email address needs to be a verified domain name in your MailChimp account. If you see a message saying that your MailChimp account doesn't have any verified domain names, follow the MailChimp instructions to verify the domain.
What Happens When Someone Unsubscribes?
When someone unsubscribes, they will not be removed from the list in People, but they will no longer receive emails.
Unsubscribing from an email takes them off the list in MailChimp. This doesn't affect the list in People, but the person will no longer receive emails for any of the lists you have in People unless you sync People to a different MailChimp List since the lists in People are sent over as segments within the main list in MailChimp.