How to Sending encrypted email attachment

Hello Experts

I need to mail of text file attachment in encrypted format with the extension TXT.ENC.

I have created one program, in SOST mail attachment have extension book1.txt.enc

But it is not the encrypted one.when we open the attachment its a text file

without any special characters or encrypted version. One more observation

there is no attachment type ENC in database so how to go about it to mail

encrypted text file or is there any other provision to send encrypted file

in mail. What are the basic requirement from Sender and receiver side.

Eg for decryption , decryption logarithm should be there at receiver's end.

Thanks

Nishi