I got a thawte Wildcard SSL-Cert for for *.my.example.com.

Now I would like to use it for my mailserver (hostname: test.my.example.com).

I edited the /etc/postfix/postfix_default.pem and included key, cert and ca in this file.

Unfortunately SSL-checks are failing with error

Unknown Authority


Cert NOT VALIDATED: unable to get local issuer certificate

What do I have to change in my config?

| improve this question | | | | |

Postfix has a perfect documentation. For your subject: http://www.postfix.org/TLS_README.html

In particular, you have a problem because Postfix couldn't find a complete certificate trust chain up to trusted CA. You have to provide that chain with your end server certificate.

This means you have to include all intermediate CAs into certificate bundle you provide to Postfix, end server certificate being first, then all CAs from bottom to top-level:

cat server_cert.pem intermediate_CA.pem > server.pem

We implemented key into own file, so my configuration looks like this (in main.cf):

smtpd_tls_cert_file = /path/to/server.pem
smtpd_tls_key_file = /path/to/server.key

Of course, key file should be kept secure, available for read only to root (Postfix starts as root, reads it and then drops privileges). You can include certificate chain and key both in a single file and then specify same file in both settings.

This is only "smtp server" (smtpd) configuration. Postfix has also a smtp client (which is used when is connects to other server to transmit mail there). It also needs own configuration, probably you have to use another certificate. Server certificate should have "ssl server" purpose, while smtp client certificate will need "ssl client" purpose. See manual page I linked to for details.

| improve this answer | | | | |

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.