Though we strive and work hard for 100% perfection, it simply does not happen. Every now and again, a few out of thousands, a card will land somewhere it should not. Here are the reasons that might happen...
1) Our system might have had a hiccup.
2) One of the browsers temporarily blocked the sending of cards from our email sending company. For example .aol might be giving "Sendgrid" a little challenge that might take a day to figure out.
3) Or, and this has happened, the subscriber put in the wrong address or put an apostrophe on the address by mistake.
4) Or, we did send the card and your friend never bothered to open it. It hurts, but it is real