Plain text file pipelined to Linux mailx turns to “Content-Type: application/octet-stream” (an attachment)

Plain text file pipelined to Linux mailx turns to “Content-Type: application/octet-stream” which is recognized as an attachment by some email client. The command is like this: $ cat log.txt | mail -s “Updated log file” -r “from@example.com” “to@example.com” I expect it to be: Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit But it turns out to be: Content-Type: […]