Changing the reply address might not help all the problems. But it will almost certainly help some. 'dontreply' in an email address is a red flag to spam-blocking heuristics.
I don't know the details about the setup of LiveJournal's mail servers, and I don't know what it would break if we changed that email address. But it's just a simple change in ljconfig.pl.
My suggestion for a change would be email@example.com, with the corresponding username lj_comment flagged as not available for use.