Deleting old LJ e-mail addresses
It appears that you can now remove those addresses.
FYI, and get on that, folks.
(I had *three* addresses I no longer controlled on there, which are thankfully gone now. Apparently in 2002-2004 I was quite the web-based e-mail whore.)
ETA: It doesn't appear to be available to everyone, and as noted in comments below, this *does* leave open another huge security hole. So, I suppose, if you're able to remove inaccessible e-mail addresses from your account, do it while you can because the change might be rolled back.