I worked at Zendesk on the email team. I think that's just support being support. The core engineers knew what they were doing.

I transitioned Zendesk from their original Exim-based ingress/egress SMTP services to Postfix and set up all the DKIM and SPF stuff long before there was ever a mail team. I worked regularly with large email providers to ensure our egress CIDR blocks were clean.

I like to think I knew what I was doing. :-)

That's good to know you knew what you were doing! However the product also didn't appear to expose any of the control we needed to have a good email setup. Maybe this is because we weren't paying enough (mentioned in another reply), but we were also never directed to pay more despite asking for this sort of control.