What a difference your choice of banks makes (don't choose Wells Fargo)

[Nutria]

And I guess stuffing a check into the envelope....

That was automated decades ago.

[kork13]

That was automated decades ago.

lol shows what I know

[Petunia 100]

Is payment processing like this (ACH and/or bill pay) not entirely automated? At what point would the be a human in the loop, except perhaps as a periodic audit to ensure the system is functioning accurately? And I guess stuffing a check into the envelope....

I would think the process is going to vary quite a bit from one organization to the next; that was my experience. But all of that data is stored someplace, for years, and sometimes printed for various reasons. People who work in payment processing, accounts receivable, customer service, IT, records management, janitorial staff, be they employees or outside vendors, could easily have access to at least some customer bank account information.