[:SettingSSLCertificateDetails:Setting SSL certificate details]
[:ChainedSSLCertificates:Chained SSL certificates]
[:CertificatePerProtocol:Set a SSL Certificate per Protocol]
You can have both the certificate and the key in one file, but you must still mention the file for both conf settings, like so:
ssl_cert_file = /usr/local/etc/ssl/private/dovecot.pem ssl_key_file = /usr/local/etc/ssl/private/dovecot.pem
Because the secret key is now part of the certificate file, it should not be world-writable.