Marketing should get their own (sub)domain for sending their missives, that way the primary corporate domain's reputation is not harmed.
Unless you want to run the risk of outgoing e-mails from Finance / Accounts Receivable to be sent to other companies' Junk folder.
There's a difference between one and dozens, and even between one dozen and dozens.
Most companies are not of Microsoft's size either: just having news.example.com would probably be sufficient for a lot places.
Security: "We had to cancel every single one of those sales because they came from stolen credit cards. It's costing us more to deal with that then we are earning"
I’ve abandoned that role and have gone back to an IC role and I’m much happier for it.
If you do it this hacky way - we run this risk and this bad thing can happen etc. After a few times they see the consequence of their decisions people start paying attention to you. Do it a few more and now the company will have an "institutional knowledge" that you are usually right, and even if the manager leave, you still end up like the go-to guy on how to ship.
And sometimes the marketing people might end up being correct! I've once actually battled to "do the correct thing" (way back in the day it was a ruby on rails modeling I think) and the product owner was like - just do it this hacky way I don't care ... I did it the hacky way and you know what - it was the right call - we never changed it again and the business knowledge we got from it was actually valuable.
I'm pretty bitter about it all still, but it's a combination of a lot of things beyond this particular bit I shared. All I can say is I'm glad I am no longer in that role, it was slowly killing me.
Now that said, I've worked with a lot of IT/engineering people who are pretty obstructionist to normal business operations and sometimes need to be told, "yeah, we're accepting the risk, move forward with the plan." Sometimes it's for good reasons, other times it's just our normal humanity asserting itself in different ways. It's a hard problem for sure.
I ran into this helping a friend whose biz emails to gmail recipients were getting dropped; the IT dept of the umbrella corp wouldn't respond. Same to me when I sent the correct DMARC, SPF etc.
(My friend's biz was his own but it shared some resources with a larger corp.)
I eventually realized that the (wrong) DMARC reporting domain wasn't even registered. I did what you'd expect and I soon had DMARC reports for subsidiaries of the umbrella corp. My friend passed that up to the CEO and suddenly IT was responsive.
In the end, it turned out that IT was deliberately blocking his biz emails to his biz family members. After 10 years they suddenly decided that email to family+gmail was risky and that they were going to gaslight my friend about it. Because reasons.
I’ve run into outright malicious stuff internally like this, but never externally - I would probably go apoplectic if I was your friend