If you send your message through just one remailer and unencrypted, the remailer operator (or somebody monitoring their email traffic!) knows both where the email came from, where it is heading and its contents. No privacy, no anonymity.
To prevent this, you have to chain at least two remailers and encrypt the message using OpenPGP. To encrypt the message, you have to know the remailers' public keys.
Find and Import the Public PGP Key of Your Remailer
To find and import the public key of your remailer: