Sending credit card info in emails can be tricky. If you put it all in one email anyone who intercepts that email, and it isn't hard to do, can read the info. If sending "secret" info by email, one of the easiest ways to make it more secure is to send it in multiple messages. The first would have an explanation of how it was split, and how to reassemble it, with the info itself in later messages. For a credit card, my suggestion, which I have used, goes like this:
First message: Name - since they have to know who you are anyway, and type of card. Neither is any secret. It can also include your order and any related messages.
Second message: I have a Visa card. I sent the first and third 4-digit groups with the validation code. Nothing in the message said what the numbers were, just three groups of seemingly random numbers. It also had my first initial and last name, not enough to use the card.
Third message: The second and fourth groups, similarly unlabeled, and the initial and name, with a confirmation of what I was ordering.
In this case, it was to a well-known online hobby shop, and they kept the info on file, so it doesn't need to be resent in the future.
