I am trying to figure out what I have done wrong. I have a certificate from PositiveSSL for my email server. I have the root certificate and the intermediate certs installed in /etc/ssl/certs/. However, I still cannot verify my certificate. I can't figure out what I have done wrong. I've been wrestling with this for a long time, and I am out of ideas. I am not that familiar with ssl certs - they usually "just work". This one, however, is kicking my butt. an at yan-ThinkPad-W530:~$ openssl s_client -connect mail.seiner.com:587 -starttls smtp CONNECTED(00000003) depth=0 OU = Domain Control Validated, OU = PositiveSSL, CN = mail.seiner.com verify error:num=20:unable to get local issuer certificate verify return:1 depth=0 OU = Domain Control Validated, OU = PositiveSSL, CN = mail.seiner.com verify error:num=27:certificate not trusted verify return:1 depth=0 OU = Domain Control Validated, OU = PositiveSSL, CN = mail.seiner.com verify error:num=21:unable to verify the first certificate verify return:1 --- Certificate chain 0 s:/OU=Domain Control Validated/OU=PositiveSSL/CN=mail.seiner.com i:/C=GB/ST=Greater Manchester/L=Salford/O=COMODO CA Limited/CN=COMODO RSA Domain Validation Secure Server CA --- Server certificate -----BEGIN CERTIFICATE----- MIIFUTCCBDmgAwIBAgIQQZM9mOpCf6BQO3apU1Xk4jANBgkqhkiG9w0BAQsFADCB kDELMAkGA1UEBhMCR0IxGzAZBgNVBAgTEkdyZWF0ZXIgTWFuY2hlc3RlcjEQMA4G A1UEBxMHU2FsZm9yZDEaMBgGA1UEChMRQ09NT0RPIENBIExpbWl0ZWQxNjA0BgNV BAMTLUNPTU9ETyBSU0EgRG9tYWluIFZhbGlkYXRpb24gU2VjdXJlIFNlcnZlciBD QTAeFw0xNTEwMDEwMDAwMDBaFw0xODEwMjYyMzU5NTlaMFMxITAfBgNVBAsTGERv bWFpbiBDb250cm9sIFZhbGlkYXRlZDEUMBIGA1UECxMLUG9zaXRpdmVTU0wxGDAW BgNVBAMTD21haWwuc2VpbmVyLmNvbTCCASIwDQYJKoZIhvcNAQEBBQADggEPADCC AQoCggEBAKzE7KEEg4I5zIkNa9PzNvDXJLJ0jFb+BXrC80CP0WgcnzDk4+M2tp9I WK3h8zHVAMj4mIUbzZYYYys0J5WyjlGclk6bPnYcuCyhyZkeevq3ZkIEbNPNlO2K ao0K9kjuLZomIPVaXsp2xtHuWU6u/Sz+XXIvlTaLuLxM6p74Z8R7DyM3iMa3/8XN 1OT624BKq6xFCas1gMPjAsLrCltDAkQIAT3pute2IsnoL082HSL0Lz8IEPELvwX0 eEmJrkB9mKvk6OoQApaZT1nZlUKtP/xfQSRt8dajR+IJWBkTG8zcWPwgReWgW5nZ 3hT07SKvYsCQO0LU6lxsQmn4UwH74GMCAwEAAaOCAeEwggHdMB8GA1UdIwQYMBaA FJCvajqUWgvYkOoSVnPfQ7Q6KNrnMB0GA1UdDgQWBBS7eRbyTVxk3hndQRXlC46K ExFddDAOBgNVHQ8BAf8EBAMCBaAwDAYDVR0TAQH/BAIwADAdBgNVHSUEFjAUBggr BgEFBQcDAQYIKwYBBQUHAwIwTwYDVR0gBEgwRjA6BgsrBgEEAbIxAQICBzArMCkG CCsGAQUFBwIBFh1odHRwczovL3NlY3VyZS5jb21vZG8uY29tL0NQUzAIBgZngQwB AgEwVAYDVR0fBE0wSzBJoEegRYZDaHR0cDovL2NybC5jb21vZG9jYS5jb20vQ09N T0RPUlNBRG9tYWluVmFsaWRhdGlvblNlY3VyZVNlcnZlckNBLmNybDCBhQYIKwYB BQUHAQEEeTB3ME8GCCsGAQUFBzAChkNodHRwOi8vY3J0LmNvbW9kb2NhLmNvbS9D T01PRE9SU0FEb21haW5WYWxpZGF0aW9uU2VjdXJlU2VydmVyQ0EuY3J0MCQGCCsG AQUFBzABhhhodHRwOi8vb2NzcC5jb21vZG9jYS5jb20wLwYDVR0RBCgwJoIPbWFp bC5zZWluZXIuY29tghN3d3cubWFpbC5zZWluZXIuY29tMA0GCSqGSIb3DQEBCwUA A4IBAQAWAEcGiQmPdeaFvK+oGumzeecVdmXYbYfuQ71kFrlmH+O/Ju9beKcF+D4D ZiybDREpzG9p3u2sCVhExttL1QL4tJejMnsIupnzNtWcFZfVt4c8Sf0ed8Q+DL91 vTjrBQ5t2sRVzqfMYv+VC/TCK/5bQwcGwfKRKP7JNwBSz3/QBN6UhJfaiN6gzMSQ s7Mn6Et4xrkiyeJIrxEgkdiStccH9EDZP9ZSY9SEd4xLHopKF9Mvkt/2Wrkmv4Az Kn+zccB8XDaceNgAw3AMwg4bLLK5u9T96cKQ3Eo4E1yvdVMmHNeP5t/Teb0xoTsT hAol+K8Jw30Oi3rLOYHiug5InS6m -----END CERTIFICATE----- subject=/OU=Domain Control Validated/OU=PositiveSSL/CN=mail.seiner.com issuer=/C=GB/ST=Greater Manchester/L=Salford/O=COMODO CA Limited/CN=COMODO RSA Domain Validation Secure Server CA --- No client certificate CA names sent --- SSL handshake has read 3057 bytes and written 698 bytes --- New, TLSv1/SSLv3, Cipher is DHE-RSA-AES256-SHA256 Server public key is 2048 bit Secure Renegotiation IS supported Compression: NONE Expansion: NONE SSL-Session: Protocol : TLSv1.2 Cipher : DHE-RSA-AES256-SHA256 Session-ID: E685C52BC4BB67DA59B0CB7B5EF99D3CD64A70C7209E2D7AFF964B0671CA7878 Session-ID-ctx: Master-Key: 04DE100CFDE53A47F9220EEDE393F026680F0543309EA1CD327B2AB088AB8529D6C2E2FB68223308E84EB3F07BCBBD2D Key-Arg : None PSK identity: None PSK identity hint: None SRP username: None Start Time: 1443956465 Timeout : 300 (sec) Verify return code: 21 (unable to verify the first certificate) --- 250 HELP