Here's a simple way to encrypt the contents of a message using the crypt command. The security level is fairly weak but it's not meant to be PGP. Here an example to encrypt and decrypt the contents of a file.
To encrypt
Encrypt with mykey in the open
# crypt mykey<not_encrypted_file>encrypted_file
Prompted for mykey
# crypt<not_encrypted_file>encrypted_file
Enter key:mykey
To decrypt
Decrypt with mykey in the open
# crypt mykey<encrypted_file | more
Prompted for mykey
# crypt<encrypted_file | more
Enter key:mykey
Mail the encrypted file as an attachment
Use a mail client such as Netscape, FireFox, or dtmail because it's easier to move the binary file.
#dtmail