If you are sending sensitive and secret data we encourage the use of: https://privatebin.net/ This ensures the data is transferred securely, and not sent in clear text together with other information.
We encourage you to use the "Burn after reading" function, so that it will only be possible to read once.
After you have hit "Create" in the top right corner, you are presented with a URL to the content you just created. Copy that URL and send it to the recipient.