Use unique reply addresses for each message
From Planfix
If you select this setting, a unique address will be added to the Reply-to field for each message from the task.
This option can be configured in the section Account Management / Email Management / External Contact Notifications:
This parameter ensures that the response to these messages will end up as part of the task, even if the mail delivery agent or server used by an external contact incorrectly processes data in hidden email headers. This setting does not usually need to be activated.