[Exim] header verify

Hi. After I put header_verify = true in my config, i noticed a bunch of
refused mail with this info:
----------------------------------------------------------------------------
--
2001-02-08 23:03:19 14R4mD-000BOD-00 rejected from (investools.com)
[209.31.31.77] <some@???>: syntax error in 'To' header: malformed
address: <me@???>\n may not follow me@??? : failing address is:
mE@??? <me@???>

I am guessing its because there are no quotes "" around first email, but
wanted to make sure, if it is really illegal to have such headers ?