SMIME email decryption using a private key – what am I doing wrong?


I have an encrypted .eml file and a private key. I’ve looked it up a lot on the internet but couldn’t find a way to decrypt the email using OpenSSL. I’ve tried this command:
smime -decrypt -in encrypted.eml inkey privatekey.key -out decrypted.eml
and each time I get this error:

OpenSSL> smime -decrypt -in encrypted.eml inkey privatekey.key -out decrypted.eml
No recipient certificate or key specified
smime: Use -help for summary.

I have also tried converting the private key to a .pem file but it still displays the same message. both files are in the same folder as the openssl.exe application is, before that I couldn’t get it to work at all.

I clearly am doing something wrong, what is it exactly?