In my Odoo 13 I get with every fetchmail request two empty emails from previous customers. When I change the frequency of the fetchmail service (Settings-technical-Automated services) I get mails accordingly. (288 if it is set to every 5 min, and 96 if set to every 15 minutes for each of the 2 mails each day)

Is there a way to find out why it is happening? At least to me it can't be external otherwise the number of mails wouldn't change with the period of the fetchmail sevice.

Is there a way to fix it?

Or if not is there a way to scedule an automatic a service which deletes all mails from test@test.com with the subject "test". A sample code would be really helpful here.

Any helpo would be greatly appreciated. It really drives me insane.