If your card recipients are not receiving your ecards, it is worth bearing in mind that they will receive a notification email to confirm they have been sent an ecard. Sometimes those can go into their email junk/spam folder - if you are concerned that your ecard has not been read, it might be worth checking with them to see if the notification email has been flagged as spam by their email provider / application (e.g. Outlook / Thunderbird etc.)
There's some extra information to help you with unread ecards on this page.
There are also a lot of answers to common questions on the FAQ page.