SMTP servers are the email accounts from which mails can be sent to contacts/recipients. You can add multiple accounts to the software; the software will use them to send emails and rotate them automatically after every mail sent. Adding SMTP server is a one time activity.
There are certain settings to be done while adding the sender account. Like you have to set the port (which is usually 587) post setting the user and the password of the SMTP. If other settings are required software will popup/indicate at that point.
Check the importance of exercise files and tutorials when creating html emails for effective marketing of your products and services.