After nginx install still port 8065 open

Hi,

I'm new to Mattermost and not a pro sysadmin. My question might be a bit stupid or missplaced.

After I folloewed the install instruction the port 8065 and nginx is serving Mattermost since a few weeks, I wanted to secure the installation and shutting ports except 80 and 443.
I saw, atht 8065 is still open.

My idea is to close this port for external usage (everybody except from localhost or 127.0.0.1)
Is this possible or will this break my installation?

Thanks a lot for your answer and help.

Marcus