The Replied value says how many people replied to your mailing you sent through email marketing app. 

To track the replies of your mailings, the reply email address has to be an alias address. 

Then, the replies to your mailing will automatically generate a new lead or a new opportunity according to the email aliases you will set. 

For example you can: 

• Use the lead/opportunity option

You can use the sales team aliases and you can follow this documentation: https://www.odoo.com/documentation/14.0/applications/sales/crm/acquire_leads/generate_from_email.html 

Find here an example with a sales team alias email

Steps to follow 

1. CRM > Configuration > Sales teams > select the sales team to which you would like to assign the new opportunities that will come from the email replies > and add your email alias. Copy your email alias (Ex: info@yourcompany.example.com).

2. Go to Email marketing app > mailings > create a new mailing > go to the settings tab and paste the email alias just created before in the “reply to” field. 

3. All your replies will create a lead or an opportunity according to the configuration of your sales team selected. The reply to the mailing will be included in the new lead/opportunity and you can reply directly from the Odoo chatter.