Right now, if I'm on a mailing list (say, bicyclists@asdf.com) and a message is sent to both me and the mailing list, I get the message twice. It'd be nice if Proton either never shows me the second message (strongly preferred), or marks the duplicate message as read once I've read one copy of the message.

This happens frequently when someone replies to a message I've sent to a list, because they hit Reply-All.