In my humble opinion, all records of the OC are by law available for viewing by any authorised individual. So a search of the correspondence would (should) show Costas letter.
However, provided this us not a frivolous claim, and is supported by some evidence the EC should be mature and smart enough to not name names.
do you have good evidence, maybe photos or other proof that the target of your claim is actually the perpetrator?
And are you sure they are really breaching a bylaw, rather than just doing something that annoys you?
Robert