SPAM - How to put List-Unsubscribe header?

Hello,

Our emails reach into Spam folder of the opposite site. I tested our mail server, it showed me the following notification. Can you help me please how I can add it? Thank you.

There is no List-Unsubscribe header.
Using an email tool that allows you to alter email headers, add the List-Unsubscribe header with the appropriate mailto and/or link for receivers to unsubscribe with.

Checkout the search function, this has already been discussed: Add "List-Unsubscribe" header in Exim config

Here is the general answer so far, because I will make this adjustment as well, I will make detailed instructions within 3 days.
https://www.roundcubeforum.net/index.php?topic=25068.0

nano /etc/roundcube/config.inc.php 

Include additional_message_headers

And then rename:

to /config.inc.php and change as you want.

This will work fine how ever if you send mail via outlook or Thunderbird it will not work you have to go with the exim routeā€¦