The thank-you email is unnecessary.
Let’s say I send you a medium-length message requesting information. You reply with a medium-length message of your own, supplying what I asked for. We both know my inquiry was satisfied with your response.
There’s no need for me to write back with nothing more than, “Thanks.” People are inundated with email all day long. Slogging through “thanks” over and over again only adds to the time we spend shackled to the “check/reply/check” machine. You know I’m grateful for what you’ve done. I express that gratitude by failing to sap another few seconds from your life with a unnecessary email.