Disable Adding Partner as Follower
While using the “Send a message” feature in Odoo records, every recipient of the message automatically becomes follower of the record,if they are not followers already. Becoming a follower means the recipients of the email, especially customer, subscribes to the document automatically. Such a subscription can be a challenge in terms of the privacy of the sales team and the company when it comes to sale and invoice records. The internal communications between the sales team will become available to the customer as well.
This app from BroadTech IT Solutions prevents adding recipients(Partner/Customer) as followers of a record while sending the message, which effectively stops auto subscription.
Please refer link to the module in Odoo Apps. https://apps.odoo.com/apps/modules/11.0/bt_disable_partner_as_follower/