I'm not sure, (RFC2822 grammar parsing is touchy stuff) but I think this email
address you posted from is messed up:
"\"\\"Marc G. Fournier From\\"@svr1.postgresql.org\":" <scrappy@hub.org>
That is, I think the display-name part of the address after unquoting is:
"\Marc G. Fournier From \@svr1.postgresql.org":
Which seems like a strange display-name and maybe not what you would have
hoped for.
In particular it seems to have confused Gnus enough so that it displays your
messages as having come from "\". That is, just the backslash.
--
greg