With a free version, you can send up to 500 emails to not more than 100 different recipients within 14 days since the start of a trial. All other paid plans allow sending more emails to more recipients within a month or a year, depending on a subscription type.

Sure, you can switch from any type of a plan to a different one anytime. Just make sure that if you found that a billing cycle should be changed and you want to get a refund for the previous one - make your decision and switch to a different plan within 14 days from an initial purchase.

All of the email and contact quota should be used within a billing period (month or a year) that is paid for. None of the unused emails or contacts will be transferred to the next billing period.