Seems like I am missing something

Yep, consumers CPU have very limited PCI lanes 16-24, the main slots (common usage graphic card ) is x16, then the cpu only have 8x lines for the rest of the stuff. Sometimes NVME or extra sata port usa some of that lines

No matter how many slots the MB have, they going to have 4 or 6 lines for the rest of the slots. Normally when there is a extra x16 is x4 only.

The best choice with consumer grade cpu/mb probably is buy a MB that support bifurcation in the main/16x slots. Probably not going to be cheap.

Then probably you going to have problems if you want connect in the future a 10gb card too, if you are planning that check used Xeon/MB normally have plenty of pci lanes (check intel ark)

I try avoid, on server sometimes its not possible.

I like Supermicro because have some ATX form factor MB with standard connectors

shelly em is probably the most used

I have mail server for years in hetzner without problem.

Probably he have the email server misconfiguration/open relay