Correct JRE version should be installed compatible with the JIRA version on the Server where JIRA is installed.
Go to the Path for JAVA_HOME is configured. You can verify at your command prompt Admin mode with:

echo %JAVA_HOME%

It would look something like this on the Server where JIRA is installed.

C:\Program Files\Atlassian\JIRA\jre\bin

Import POPS certificate on Server for mailbox connectivity with JIRA:

The certificate would be created by your internal CA. You can place it at an accessible path on the JIRA Server. Use the below command:

C:\Program Files\Atlassian\JIRA\jre\bin> keytool -import -alias rootCA -keystore "C:\Program Files\Java\jre1.8.0_91\lib\security\cacerts" -trustcacerts -file "E:\Certificates\POPS.cer"

Download SSLPoke.class. Place this class at the above bin path.

Diagnose connectivity with the following command:

C:\Program Files\Atlassian\JIRA\jre\bin> SSLPoke mailserver.example.com 995

995 is the port for Secure POP and the Server name would be your On Premise Exchange Server name.

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