Comodo SAN positve SSL, where is the key

Question

Im just setting up my emailserver and want it to be SSL secured with a valid certificate, so I got a Comodo positivessl cert. As I use multiple domains, I needed a SAN cert, which I got. What is in the package I received after the process is:

<my_san_cert>.crt
AddTrustExternalCARoot.crt
COMODORSAAddTrustCA.crt
COMODORSADomainValidationSecureServerCA.crt

So from what I understood, I have to bundle the last three files, which I did, to a bundled file. Now I need to put it in the main.cf config.

smtpd_tls_cert_file = /some/path/yourdomain.crt
smtpd_tls_key_file = /some/path/yourdomain.key
smtpd_tls_CAfile = /some/path/ca.txt (bundle file)

(source: https://www.positivessl.com/ssl-certificate-support/email-certificate/postfix.php )

What I do not get, where is my keyfile? Is it the private key used for the request of the certificate?

Thanks in advance!

Answer 1

Is it the private key used for the request of the certificate?

Yes.

To expand on this and perhaps state the obvious, your private key needs to be truly kept private. Anyone who is able to get their hands on it would be able to impersonate your website.

Your signed cert and the cert chain, on the other hand, are fully public, and can be freely downloaded by anyone.