Translation:Not during response and transfer
I would translate this to "Not when answering or forwarding".
Let me try to put this into context: Suppose you have some email program in which you can change the formatting of the text only when you're writing a new email (I agree that would be terrible....). Someone asks you "Kann ich das Textformat ändern wenn ich eine Email beantworte? (Can I change the format when responding to a an email?)" Then you might answer: "Nein, nicht beim Antworten und Weiterleiten" -- "No, not when answering and forwarding".
Of course, "Weiterleiten" can mean "passing on" in other contexts, and I'm sure in this sentence it can also mean "passing on".
Thank you, that is helpful. I thought it might be an idiom, perhaps a metaphor for something else. It is good to know that it is what it seems to be. (But I think I would get another e-mail program. ;-)