Top-posting
Writing your reply above the entire quoted message — standard practice in corporate email, a mortal sin on Usenet.
Usenet and mailing lists settled on a different norm early: trim whatever you aren't answering, quote the rest with >, and put your reply beneath each relevant chunk. That's interleaved quoting, or bottom-posting when the reply comes last. The reasoning was practical — a thread should read top to bottom, and every needlessly quoted line got copied to thousands of servers. Several news posting programs flatly refused articles that contained more quoted text than new text.
Once email became an office tool in the 1990s, clients like Outlook put the cursor at the top with the whole original underneath, and the rest of the world followed. The argument earned its own classic signature: A: Because it messes up the order in which people read. Q: Why is top-posting so bad?