Is there a way to get a list of all our customer's email address?

To get the list of all your customers email addresses, you need to access "Customer List Report." 

Before you start:- 

This report also includes the list of failed transactions, if you want the list of only successful customers, please ensure you select "Successful" from the "Filter Options" and regenerate the report. 

i) Simply hover the mouse cursor on the "Organization Name" at the top left and select "Customer List" from the drop-down list. 

ii) By default, the report would have the "All Time" date range auto selected, if you would like to customize it select from the various options at the top. 

You could create a customer list of a specific event, by clicking "Specific Events" and Selecting the event from the drop-down list. 

The report can also be downloaded in CSV, PDF, alternatively, the entire customer list report can be send to the email user you are logged in with upon clicking on "Email." 

Furthermore, you could also schedule the report to auto deliver to your email address at regular interval. 

NOTE: Only Users with permission for Customer Reports can view this in the drop-down.