Mailchimp is a web-based broadcast email application, on this platform you can create campaigns which can later be sent to your existing customers.
Currently DealPOS has been integrated with Mailchimp so you don't need to input customers from dealpos to Mailchimp manually, because all of that can be done automatically.
You can upload the contacts that are on your DealPOS to MailChimp when your DealPOS and MailChimp have been integrated. For example I choose contact with name "Dahla" :

Step 1. Go to Upload, Select Join Date, then Click Upload

Step 2. Contact was Uploaded Successfully to Mailchimp


Notes :
Here's tutorial for create new list : Create New Mailchimp List
People also read these articles :
To Integrate DealPOS with MailChimp : Integrating DealPOS with MailChimp
To Sync DealPOS Inventory to Shopify : Sync Inventory DealPOS to Shopify
To Get MailChimp API Token : Get The MailChimp API Token