A message with a recipient address that contains a non-printing character is stuck on my mail queue. How can I remove this address?

You can use the -Mmd command line option to mark a recipient address delivered , which effectively removes it. If you are using the Bash shell, you can enter non-printing characters using an escape sequence. For example:

exim -Mmd 15HKvU-00013Q-00 $'\240'abc@x.y.z

In this example, the first character of the local part has a code value of 240. If you are using a shell that does not support this, create the command in a file and run it as a shell script.