Bonjour,I have a question

I have a question: If I have several accounts that have the same password and I know the email address they are tied to, are there restrictions and penalties for mailing materials and items between accounts? What is the threshold value for the restriction?
The reason for this is that I have only one main character per account, and the others are created to be used as storage. It would be too cluttered to have all these characters in one account.