do you receive other Email coming from Tableau Server when you subscribe to a view for example? Or do you even have this subscription option available for any view on the upper right side ?
Tableau Server configuration allow you to configure a SMTP Server to distribute Email an alerts as you wish. If you do not receive other Emails coming from the server it may be because of an error in the SMTP server configuration. It could be because of a firewall blocking the access to this mail server and Tableau server.
That is the first things that comes to me in mind so I hope it helps...
BR regards and good luck