Send your name and address in a separate e-mail from your credit card numbers. Sending separate e-mails lessens the chance of your credit card information being intercepted by hackers. Each e-mail goes through different servers before it reaches its destination, and rarely do two e-mails take the same path.
Type your credit card numbers out. Instead of "6" type "six," for example. This prevents the possibility of a keylogger on your system intercepting your credit card numbers. Keyloggers are malicious software that record keystrokes, store them to a file and send the file off to remote attackers. Most attackers pay attention only to numbers, as these are often associated with credit card numbers and passwords. Typing your credit card numbers out avoids this.
Divide your numbers into different e-mails. Either split the numbers in half, sending a group of eight in one e-mail and the rest in another, or four numbers in four different e-mails. If a hacker does intercept one e-mail, he doesn't have the full information to use your card.
Ask for a confirmation e-mail. Request a confirmation e-mail that all of your information has been successfully received by the merchant or whomever your sending your information to.