Peter,
By "Cost of doing business" I didn't mean literal cost, like dollars or Euros, but in precisely time and aggravation. Once you solve this issue, another one will pop up with another email, or something similar. Or, someone will spoof our email and someone totally unrelated to our group will complain. That's why it's "never ending" and you don't rest on this...
It is quite akin to anti-virus work done in the IT world. As soon as they kill one virus, some hacker somewhere else creates another...they cannot rest.