The pricing scheme is very simple; for each email account you want to use in the integration, you pay 1 EURO per month per email, but you don't have to pay every month for each email you may have, instead you purchase credits. Each credit gives you right to use any email you want in coreBOSMail.
Once you have purchased some credits you can assign them to your different emails. If one of your emails is no longer in use, you simply free the credits assigned to it and assign them to another email very easily.
Both the purchase and the assignment of credits is done in the coreBOSMail backend along with the creation of emails which can access the program. You can get more information on how to purchase credits and assign them in the How it works section of the website.