Striving for a medal in the Passive-Aggressive Olympics

When I worked for OldBoss, I often ended up doing support tasks for other people who had assistants of their own. This generally happened because they were trying to "coordinate" their travel or registration with that of OldBoss, so it was just easier all around to dump the whole thing on me to do. When I got tasked with the short term "project detail" supporting OldBoss until the organization firmed up some new high-level staffing, I began the juggle of prioritizing the aspects of my regular job that were part of my job description (i.e., considered when my annual review is done this summer) with the tasks necessary to support OldBoss (i.e., what I will probably not get credit for doing anyway). OldBoss has found a new job. Some of his upcoming trips and responsibilities are being taken over by others within the organization. One of these people is one of the folks who used to dump their administrative tasks on me. Is it so wrong that I go out of my way to make sure that all the email traffic back and forth about what I cannot accomplish for said dumper because it violates the laws of time and space, and all the messages in which I let him know how he will have to do certain things on his own, end with my full signature block (the signature block that has my title, which no longer contains the words "administrative" or "assistant," and my department, which is completely separate from the division in which said dumper works)? Since I can't have the email read "Listen up, whiny-head, the fact that I'm even thinking about helping you is a favor in and of itself, so shut up and make your own secretary do this crap for you!" I can at least remind him that I don't answer to him, and he has to go aaaall the way up the chain of command before the two of find a common boss.