Insincere thank-yous are an important part of legal communications, so keep things fresh by mixing in new disingenuous messages of appreciation when you have the chance. Instead of sending a "Thx", try a "Tx" or a “TY” occasionally. Or maybe a "Thanks so much!" instead of a "Thanks again!" If you are having a bad day, you might try a “Thanks.” If you want to say thanks without actually saying thanks, you might add an inappropriately long ellipsis at the end like this, “Thanks. . . . .” A preemptive "Thanks in advance" before anything even happens is also a nice touch.