One key concept to first understand is that you should not buy email lists from any third party vendors. You should not even set up email campaigns and send emails to these purchased lists. The one simple reason is that these people in the lists do not know you and/or your brand/business. Receiving emails from some strangers would always result in extremely low open rates. You do not know how many of the email addresses in a purchase list are still valid email addresses. When you send any emails to the list, the deliverable rate would be very low.
A purchased list would almost certainly cause a problem with your email service provider regardless of which provider you have chosen to use. Your email service provider would know exactly who you are sending emails to, and they know the exact results that your campaigns get. When it is a purchased list, it would take really short time with data mapping for your email service provider to figure out you are indeed sending a large amount of emails to some third party purchased list. Many email service providers nowadays do have past performance of other campaigns. Based on the historical data, they would build their blacklisted email addresses. Through this, you plan to use a purchased list would quickly fail.
Mailchimp, Getresponse, Aweber, and a few other similar tools are great for doing a simple tasks on a regular basis: Sending emails to your contacts (or lists). Normal email campaigns can work well up till a point, and it will gradually lose its effectiveness. You will be relatively less efficient when you have to send each email to a list of contacts each time. You would well be more efficient if the tool actually can figure out your next steps.
Here comes the concept of marketing automation for email campaigns. One of the tools that allows you to run marketing automations with your email campaigns is Active Campaign. Another tool that does similar is Sendinblue. There are a few more email tools that would do similar and still work pretty well.
When sending emails through your campaigns, whether it is a normal email campaign or an automated email campaign, it is important to segment. Segmentation of contacts could be achieved by using multiple lists, or many meaningful tags. Proper segmentation of lists or contacts would ensure better campaign results.
Another useful and effective method is to run split tests with your campaigns. It can be done by manually first separating your lists perhaps with different tags. Some of the email service providers also provide the capability or feature to set up and run split tests on email campaigns.