[layer8]

The correct thing to do is to send a 552 5.2.2 Mailbox full [0][1], not to delete the account. Email account quota is a standard feature of mail servers.

[0] https://en.wikipedia.org/wiki/List_of_SMTP_server_return_cod...

[1] https://www.rfc-editor.org/rfc/rfc3463.html#section-3.3