The encrypted message is revealed to, and can be altered by, intermediate email relays. In other words, the encryption takes place between individual SMTP relays, not between the sender and the recipient. This has both good and bad consequences. A key positive trait of transport layer encryption is that users do not need to do or change anything; the encryption automatically occurs when they send email. In addition, since receiving organizations can decrypt the email without cooperation of the end user, receiving organizations can run virus scanners and spam filters before delivering the email to the recipient. However, it also means that the receiving organization and anyone who breaks into that organization's email system (unless further steps are taken) can easily read or modify the email. If the receiving organization is considered a threat, then end-to-end encryption is necessary.