Benefits of using a subdomain for sending email?

My question is: Is there any added benefit of sending automated email from an email address with a subdomain?

I don't think there are many technical reasons why a subdomain is required or necessarily better for deliverability of emails.

That being said, having/using subdomains can sometimes make things easier for large organizations because:

• As an admin, I may not have access to global resources associated with the primary domain. For example, maybe I only manage IPs/Firewalls/DNS Zones in my specific regional office/division.
• Even if I did have access to global resources, the scope of users/systems affected by my email changes is large. Perhaps I don't want that.
• Even though we're specifically discussing outbound deliverability here, there is still the possibility of NDRs and failed delivery generating return traffic. Depending on the volume of mail I'm sending, I may not want delivery status notifications going back through my standard inbound mail route.

Ultimately, I think it comes down to the use case here and scope of systems affected.

A big advantage is that most email spammer-blacklist organizations treat subdomains separately. So, even if your automated e-mail subdomain gets blocklisted (PC term for blacklist), your main domain will still be able to continue sending e-mails. This is actually pretty important, because even the most innocent newsletters/automated replies get flaged as spam by some receivers. And this can eventually lead to being blocklisted.

Also, having a subdomain makes tracking reputation separately possible.

An interesting interview can be found here with spamhaus: Spamhaus Provides Answers Part 4

Question number 32 is talking about subdomains and how they are treated separately (unless more subdomains from the same domain get blocklisted, which might lead to the whole domain getting blocklisted).