Article ID: 122732, created on Aug 28, 2014, last review on Feb 22, 2016

  • Applies to:
  • Plesk for Linux/Unix


For some reason it fails to connect to the server over SSL/TLS. If no encryption is used, connection goes through fine. When checking with

openssl s_client -starttls imap -crlf -connect localhost:143


openssl s_client -connect localhost:993

get one of the following error message

depth=0 /OU=Domain Control Validated/OU=EssentialSSL Wildcard/CN=*.domain.tld
verify error:num=20:unable to get local issuer certificate


verify error:num=27:certificate not trusted


verify error:num=21:unable to verify the first certificate


Improper CA root certificate used or certificate chain is corrupted


If 'GoDaddy G2' certificates are used, download 'GoDaddy Certificate Bundles - G2' from

If you are using certificates from another SSL certificate provider, then you should obtain an appropriate CA certificate bundle having intermediate root CA included.

  1. Modify '/etc/courier-imap/imapd-ssl' and set TLS_TRUSTCERTS=/path/to/the/certificate/bundle/file
  2. Modify '/etc/courier-imap/pop3d-ssl' and set TLS_TRUSTCERTS=/path/to/the/certificate/bundle/file
  3. Modify '/etc/postfix/' and set 'smtpd_tls_CAfile=/path/to/the/certificate/bundle/file'

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