Sorry to hear you had a problem with the cards, Garry.
I asked Tahra if she knew what may have caused it. She said it's hard to give an exact reason for the error as it could be due to one of several things - the destination email might have been down for some reason, or the e-mail was mistyped, or the mailbox was full.
Could you please check that the e-mail is correct, and maybe send another message from an alternate e-mail address? Another reason your card might not have got delivered could be because it was accidentally filtered as spam.
Have you successfully sent cards from playkingdoms this way before using the same addresses in each field, or was this the first time you tried it?