Thunderbird Settings

Thunderbird

Choose Server Settings:

Fill in Server Name connection security:

Thunderbird Account Settings

To rely on IMAP-idle unmark:
"Check for new messages..."

Choose "Advanced..."

Thunderbird Server Settings

The change from before is that no IMAP server directory is needed. Therefore leave the textbox empty.
This server also accepts folders that contains sub-folders and messages

Thunderbird Advanced Account Settings

Last but not least: Restart Thunderbird!