I 100 percent agree to the "I'd like the function to block a domain..."
It should be common sense that block means to prevent. In this case it definately should mean block the email from arriving to my email address period. Sending blocked "items/domains" to the junk mail basically allows users to continue receiving abuse from unwanted offenders.
It would be nice if their software would give us an option that would allow mail to be deleted (or even permanent deletion) after their software detects messages that are clearly forged. It should be pretty obvious when the email shows "no sender address" (web client version) that means that it's likely to be forged. Obviously to reveal the details they are trying to hide, we have to look at the message header.
In the United States, if you want mail to be blocked, from a SPECIFIC individual, company or organization, go to the USPS. If the USPS gives some random excuse, then next step is to go through courts to file some legal action and/or form of a restraining order (or some form of "Anti-Harrassment") against the offending sender.