You should never, ever just email credit card numbers, passwords, or other private information. You don't know how many servers the message will pass through between your computer and the recipient's, or who has access to those servers. Email is only slightly more private than a billboard. (A slight exaggeration, but you get the point.)
A truly private message must be encrypted before it leaves your computer, and remain encrypted until the recipient receives it. I will show you how i send Emails and other highly confidential information without a special password. Its a cloud-based service called Sendinc.
To use this service, both you and the recipient must have Sendinc accounts. Joining is easy, and unless your messages are larger than 10MB each, or you're sending more than 20 of them a day, a free membership will do. If you send a message to someone who doesn't have a membership, they'll be invited to sign up.