-Dmail.debug property does not work for POP/IMAP

For debugging mail problems (POP, IMAP, SMTP), the JavaMail library provides the mail.debug property. When set to true, this prints protocol-level logs showing what is happening.

This works for SMTP, but does not work for POP or IMAP (eg. creating issues/comments from mail). In the library, we instead initialise the JavaMail properties from the WEB-INF/classes/atlassian-mail.properties file. So to get debug logs for POP and IMAP, you'd need to create WEB-INF/classes/atlassian-mail.properties and add the line:

mail.debug=true

and then restart.

JIRA should allow command-line properties to override those in atlassian-mail.properties, so that people don't have to set properties in a text file in a .war.