Integration with 3rd Party Mailing Engine like MailChimp and MailGet

Integration with 3rd Party Mailing Engine like MailChimp and MailGet

I wanted to understand the following.
1.  When using Zoho as the CRM, and using an external 3rd party mailing software, what workflow is followed (step-by-step)?
2.  How do I communicate, from Zoho to which contacts the mails should be sent, to the mailing engine? Does this have to be manual? What happens to the response to mailer (how do I get to know in Zoho what response has come and take action)?

Thanks and with best regards

Debashish Bhattacharyya