Imagine some bothersome emails from someone elses Mailchimp list. In order to delete a mail you have to confirm every deletion. Not much fun.
Firstly, you should decide how severe the actions itself would be. Our case - deleting a commercial email - is certainly not severe. A user would very likely not bother too much about accidentally deleting it. Hence, do not ask for confirmation. On the other end of the spectrum you have messages that relate to important personal data which cannot be recovered. Therefore, you need to show a dialog whereby the confirmation button is not - and this is important - on the expected place, e.g. for most Android and iOS apps that would be the left side of the dialog.