JIRA is unable to retrieve messages from an IMAP server and displays error messages like the following in the logs:
The Java mail library used by JIRA is not configured to use TLS for non-SSL connections by default. If you connect to an IMAP server without using SSL, and the server is not configured to allow unencrypted connections, you may see the error shown above.
There are different ways to resolve this problem:
If following options 1 or 2 below, please follow the steps on Connecting to SSL services to import the Certificate from the IMAP server in order for the connection to work correctly.
Switch to using an SSL connection to communicate with your IMAP server.
If you are connecting to your IMAP server over a non-SSL connection (using STARTTLS), set the following property to the JIRA Startup Options:
Allow unencrypted communications between your JIRA instance and your IMAP server (not recommended).