PVE usually has postfix installed as MTA.
* It's probably the easiest to configure it using your ISPs mail-servers as smarthost
* with `dpkg-reconfigure postfix` you should get asked a few questions - chose the appropriate answer and enter your ISPs mail-server as smarthost)
* set the email which should receive the mails as the email of user 'root@pam' (in the GUI->Datacenter->Permissions->Users)