[sph]

IIRC cron writes stdout to the local mail spool (<user>@localhost). If the server is configured correctly, with an SMTP service for the domain, these emails are basically forwarded to <user>@<domain>

In practice, I have never seen a Linux server with an actual SMTP server configured correctly in 20 years, so the worst that usually happens is that cronjobs never actually leave the machine. You used to get a mail notification when you logged in if cron had written something, but that doesn’t happen anymore on recent distros.

[axpvms]

Lots of domains have a locahost record set up. I used to think it was funny to use them for email forms when entering an email was required and the email validation would accept them. eg: to set the email to [e-mail] for example.

[lgeorget]

It's usually configured correctly at some point in time and then the configuration "rots": it becomes inconsistent, some emails are forwarded, other are lost, nobody cares, etc.

In my case, I configured Postfix to redirect all mails looking like (root|admin|postmaster)@server to myemailaddress+(root|admin|postmaster)_server@domain and Postfix ignores what comes after the + in the user part. So I get all the emails but I still know where they come from. It has worked well for quite some years now but I'm not deluding myself, I know that at some time, that will rot too.