Mailchimp is absolutely ideal for corresponding with customers/clientele. Not only is Mailchimp very affordable for businesses with limited budgets, it is a great way to manage and store the likely smaller customer lists those businesses have. In my personal experience, I have loved the way the "unsubscribe" feature works with Mailchimp. It notifies you as the user when and why someone requests to be unsubscribed from future correspondence, and ensures they are actually removed from your Mailchimp list. Along those same lines, mailing out to a list on a spreadsheet and/or directly from an email account often results in the message being flagged as spam/junk for recipients. You also often have limits as to how many addresses you can send a message to at one time, creating additional time and work for the user. Mailchimp does it all for you with one click of the button. Not only that, you can review analytics including how many people have opened the email, how many additional clicks links within the email have gotten, how many emails were undeliverable, and more. It is just so user-friendly. Can get pricey if you have a large subscriber list (over 2,000).