I'm trying to match strings such as "X \ n a x" which appear in spam email so I can filter. I can do this but not in a completely satisfactory way. I guess I've just gotten myself confused, but I don't understand why

$_="X ";
if(m'X\ '){print "OK1\n";}
$_='X\ ';
if(m'X\ '){print "OK2\n";}
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produces "OK1" only. I would expect the first match to fail and the second to succeed. Thanks for any comments!