With the IDLE function enabled, Mac Mail will make a continuous connection to the HG server, and this will contribute to the problem. Instead, you can configure Mac Mail to periodically check for new mail. A reliable frequency for the idle feature is every 10 minutes to ensure that Mac Mail is cleaning out any lingering processes.
To disable the IDLE feature:
- Select Mail | Preferences from the menu.
 - Choose Accounts.
 - Select the desired IMAP account.
 - Go to the Advanced tab.
 - Uncheck Use IDLE command if the server supports it.
 - Additionally, you can uncheck Include when automatically checking for new mail.