code: private String getQualifiedMailboxName(GreenMailUser user, String mailboxName) {
          String userNamespace = user.getQualifiedMailboxName();
  
          if ("INBOX".equalsIgnoreCase(mailboxName)) {
              return USER_NAMESPACE + HIERARCHY_DELIMITER + userNamespace +
                      HIERARCHY_DELIMITER + INBOX_NAME;
          }
  
          if (mailboxName.startsWith(NAMESPACE_PREFIX)) {
              return mailboxName;
          } else {
              if (mailboxName.length() == 0) {
                  return USER_NAMESPACE + HIERARCHY_DELIMITER + userNamespace;
              } else {
                  return USER_NAMESPACE + HIERARCHY_DELIMITER + userNamespace +
                          HIERARCHY_DELIMITER + mailboxName;
              }
          }
      }
docs: Convert a user specified store name into a server absolute name.
  If the mailboxName begins with the namespace token,
  return as-is.
  If not, need to resolve the Mailbox name for this user.
  Example:
  <br> Convert "INBOX" for user "Fred.Flinstone" into
  absolute name: "#user.Fred.Flintstone.INBOX"
  
  @return String of absoluteName, null if not valid selection