Do publishing houses that require submissions to come through agents read all agented submissions, even from agents who are new in the business and who may not be known to the editor? Or do editors see a package that claims to be from an "agent," check it against some actual or mental list, and discard it if they do not recognize the name? I imagine, of course, that some agents command more attention than others, but do all agents, even unknown ones, at least get their client's foot in the door?Yes and no.
I do sometimes check agents against the list called Preditors and Editors, if the agent is sending me unapologetic dreck of genres my house doesn't even publish. (Major red flag.) That is bullshit agenting, whether the agent is legit or scamming.
Likewise when we get something through the front desk beginning, "Dear Editor." Agents are supposed to be doing their damn homework and knowing who to send a manuscript to at a particular house. "Dear [Publishing House]" means that the agent knows zipola about the industry, and even less about being a good agent.
And simply claiming to be an agent is not enough. We've seen enough jackass authors pretend to be their own agents that we're well wise to that trick. Also if you're pretending your lawyer is your agent. (No, he's not.)
But in general we try to reply courteously to agented submissions, even if we haven't heard of the agent. The unknown ones are certainly low-priority, though.