Messages from bogus Safe-mail addresses marks clearly all messages pretending to be sent from another user - but are actually not from a user - in the header of the message immediately below the "From:" line:
Warning: This message was NOT sent from a user.

Spammers often send messeges claiming to have hacked into users accounts by pretending to send them from those accounts. marks these messeges as described above. However, and as was to be expected, it didn't take too long until spammers realized that we show this message and started sending such messages from addresses. Here are some more safety suggestions:
A. Set your Preferences not to accept message from addresses that are not in your Address Book.
B. If the above is not possible for you, suspect any unexpected messages.
C. You may check your Sign-in history for any Sign-in that is not known to you. Notice that this list also show failed (wrong password) Sign-ins.
D. You may look at the full header of any suspect message to see where it really came from.

The system digitally signs each and every message. This signature can be generated only by the system but it can be verified by any email system before transferring it to the recipient. Unfortunately, this is mostly ignored.
However, the system checks this signature and clearly marks messages that were not sent from users. This is true for any address at including non-existing and even your own address.

Marked messages you receive are probably fake, and you should ignore them. Please, do not read any marked messages unless you expected them.
Unfortunately we can't automatically reject such messages as there are systems that produce such messages. For example: you read an interesting article and would like to forward it to someone. Many systems supply a button to do so and among the needed fields, one is for your own email address. The correct way is to send it with "From:" of the REAL sender add a field "Apparently from:", but many systems do not do that, leading to the messeges being marked by