There's two answers to this question...
First, in terms of limits, CorpNote allows you to send as many cards as you like. Your monthly membership fee is for "unlimited" sending of ecards.
Second, there are two ways to send a single card - each having a maximum number of recipients when you click the "send" button.
For cards sent using our address book, or by manually copying and pasting email addresses, you can send to 250 people at a time. If you have a bigger list hten simply copy the card you just sent and send the copy to the next 250 people on your list. You can do this as many times as you like until all your recipients' cards have been sent. (We make it easy by giving you the option to "copy card" after each one is sent.)
For larger lists of up to 2,500 recipients you'll need to enter your contacts into CorpNote's online Address Book and create a "Group." Once a group has been created, it can be used as the address list when you are sending your cards to large numbers of people. After the Group has been created, simply select it by name on the Address/Send screen any time you want to send those contacts a message and you'll be able to send (or schedule) to all 2,500 recipients with a single click.