This produced a lot of output. In the middle of the output was the following:
verify error:num=20:unable to get local issuer certificate
verify return:0
您缺少根证书，应使用 -CAfile 或 -CApath 指定它。
然而，如果您解决了根证书问题，可能会遇到握手警报。我认为这是由于我没有客户端证书导致的问题（因此您可能不会遇到此问题）。下面的 0x14094410 是 OpenSSL 错误，SSL 错误（来自 TLS 协议）只是 SSL alert number 40。 Alert 40 是握手警报，没有其他信息。
首先
确定你需要哪个根证书：$ openssl s_client -connect gateway.sandbox.push.apple.com:2195
CONNECTED(00000003)
depth=1 C = US, O = "Entrust, Inc.", OU = www.entrust.net/rpa is incorporated by reference, OU = "(c) 2009 Entrust, Inc.", CN = Entrust Certification Authority - L1C
verify error:num=20:unable to get local issuer certificate
verify return:0
140067272132264:error:14094410:SSL routines:SSL3_READ_BYTES:sslv3 alert handshake failure:s3_pkt.c:1257:SSL alert number 40
140067272132264:error:140790E5:SSL routines:SSL23_WRITE:ssl handshake failure:s23_lib.c:177:
---
Certificate chain
0 s:/C=US/ST=California/L=Cupertino/O=Apple Inc./OU=iTMS Engineering/CN=gateway.sandbox.push.apple.com
i:/C=US/O=Entrust, Inc./OU=www.entrust.net/rpa is incorporated by reference/OU=(c) 2009 Entrust, Inc./CN=Entrust Certification Authority - L1C
1 s:/C=US/O=Entrust, Inc./OU=www.entrust.net/rpa is incorporated by reference/OU=(c) 2009 Entrust, Inc./CN=Entrust Certification Authority - L1C
i:/O=Entrust.net/OU=www.entrust.net/CPS_2048 incorp. by ref. (limits liab.)/OU=(c) 1999 Entrust.net Limited/CN=Entrust.net Certification Authority (2048)
所以您需要Entrust.net Certification Authority (2048)。 您可以从Entrust根证书下载它。 它的名称为entrust_2048_ca.cer，格式似乎为PEM。
第二步
现在再次运行openssl s_client，但这次使用-CAfile entrust_2048_ca.cer。 注意它会显示通过验证，返回代码为Verify return code: 0 (ok)：
$ openssl s_client -connect gateway.sandbox.push.apple.com:2195 -CAfile entrust_2048_ca.cer
CONNECTED(00000003)
depth=2 O = Entrust.net, OU = www.entrust.net/CPS_2048 incorp. by ref. (limits liab.), OU = (c) 1999 Entrust.net Limited, CN = Entrust.net Certification Authority (2048)
verify return:1
depth=1 C = US, O = "Entrust, Inc.", OU = www.entrust.net/rpa is incorporated by reference, OU = "(c) 2009 Entrust, Inc.", CN = Entrust Certification Authority - L1C
verify return:1
depth=0 C = US, ST = California, L = Cupertino, O = Apple Inc., OU = iTMS Engineering, CN = gateway.sandbox.push.apple.com
verify return:1
140642906502824:error:14094410:SSL routines:SSL3_READ_BYTES:sslv3 alert handshake failure:s3_pkt.c:1257:SSL alert number 40
140642906502824:error:140790E5:SSL routines:SSL23_WRITE:ssl handshake failure:s23_lib.c:177:
---
Certificate chain
0 s:/C=US/ST=California/L=Cupertino/O=Apple Inc./OU=iTMS Engineering/CN=gateway.sandbox.push.apple.com
i:/C=US/O=Entrust, Inc./OU=www.entrust.net/rpa is incorporated by reference/OU=(c) 2009 Entrust, Inc./CN=Entrust Certification Authority - L1C
1 s:/C=US/O=Entrust, Inc./OU=www.entrust.net/rpa is incorporated by reference/OU=(c) 2009 Entrust, Inc./CN=Entrust Certification Authority - L1C
i:/O=Entrust.net/OU=www.entrust.net/CPS_2048 incorp. by ref. (limits liab.)/OU=(c) 1999 Entrust.net Limited/CN=Entrust.net Certification Authority (2048)
---
Server certificate
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----
subject=/C=US/ST=California/L=Cupertino/O=Apple Inc./OU=iTMS Engineering/CN=gateway.sandbox.push.apple.com
issuer=/C=US/O=Entrust, Inc./OU=www.entrust.net/rpa is incorporated by reference/OU=(c) 2009 Entrust, Inc./CN=Entrust Certification Authority - L1C
---
No client certificate CA names sent
---
SSL handshake has read 2683 bytes and written 338 bytes
---
New, TLSv1/SSLv3, Cipher is AES256-SHA
Server public key is 2048 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
SSL-Session:
Protocol : TLSv1
Cipher : AES256-SHA
Session-ID:
Session-ID-ctx:
Master-Key: A2F375CC440179ADF831179C32A35AF4...
Key-Arg : None
PSK identity: None
PSK identity hint: None
SRP username: None
Start Time: 1398721005
Timeout : 300 (sec)
Verify return code: 0 (ok)
第三条
这是一种旧的做法，当SSLv3仍然流行时使用。也就是说，POODLE攻击是未知的：
$ openssl s_client -connect gateway.sandbox.push.apple.com:2195 -CAfile entrust_2048_ca.cer
你应该考虑切换到TLS 1.0或更高版本，并使用服务器名称指示（SNI）。SNI是TLS的一个特性，SSL中没有。你可能需要在2016年强制使用TLS 1.2，并可以使用-tls1_2来实现。
$ openssl s_client -connect gateway.sandbox.push.apple.com:2195 \
-tls1 -servername gateway.sandbox.push.apple.com -CAfile entrust_2048_ca.cer
以下是其他评论和回答中的信息，我将它们汇总以方便查看。您应该根据情况为评论或回答点赞。
客户端证书
Korbbit提供了以下的额外信息。它回答了我之前的陈述，即“警报握手失败……我认为这是由于我没有客户端证书引起的问题”。如果对您有帮助，您应该向Korbbit提供反馈：
如果您再次查看教程，您应该键入以下内容：
-cert PushChatCert.pem -key PushChatKey.pem
有了Korbbit的反馈，答案变成了：
$ openssl s_client -connect gateway.sandbox.push.apple.com:2195 \
-tls1 -servername gateway.sandbox.push.apple.com \
-cert PushChatCert.pem -key PushChatKey.pem -CAfile entrust_2048_ca.cer
ca-certificates bundle and -CApath
来自Timur Bakeyev的消息，Entrust.net是一个著名的根证书颁发机构，因此它的证书包含在常见的CA证书捆绑包中（在Debian中是ca-certificates）。通常情况下，它会被安装到/etc/ssl/certs目录中，并且可以用-CApath /etc/ssl/certs/选项进行引用。
您可以使用-CApath代替-CAfile，方法如下。
$ openssl s_client -connect gateway.sandbox.push.apple.com:2195 -CApath /etc/ssl/certs/
