while i was playing message message with a person, he told me that his account is used by other creed players too. i accidentally deleted the mail, is there a way to get that mail back? what will happen to him/her for doing this? as far as i know, different people using same account is wrong, isn't it?

it is wrong and as far as i know we cant retrieve deleted messages

then, perhaps, i can't do anything, because the proof is gone. but nothing matters, it is possible that the original person wanted to leave pokemoncreed, so he left it for a friend. everyone has their own reasons

yeah you could be right

Doesn't matter the reason. It is not allowed. If catches doing this you will most likely be banned along with your other accounts/IP addresses.