authorized senders only

It is useful when you want to receive emails from one sender only,
and all messages that fail the checks must be discarded.

In this case you need to be sure that the sender’s email address has not been spoofed.
This control can be done putting together SPF and DKIM authentication.

SPF confirms the sender’s address and its relationship with the server that sent out the message.
DKIM guarantees that the email (including the attachments) has not been modified since the “signature” was affixed.

In theory it’s that easy, in practice both SPF and DKIM can refer to a different domain than the from address.

We check that SPF authentication and DKIM signature are related to the domain in the from address.
In this way no other than the original sender can authenticate the email. This guarantees its origin.

remove dangerous attachments

The “remove dangerous attachments” option blocks all potentially harmful attachments
except some safe extensions as pdf, txt, gif, jpg and png.

The recipient receives the message without the attachment.
A warning is added to the beginning of the content, like this:

WARNING: This email violated Your Company's email security policy and
has been modified. For more information, contact your IT Administrator.

An attachment named "example.zip" was removed from this document as it
constituted a security hazard. If you require this document, please contact
the sender and arrange an alternate means of receiving it.

On the internet there is an interesting case study, that ends with this sentence:
“For us, attachment filtering has been very successful”
– web.mit.edu/net-security/Camp/2004/presentations/reillyb-mit2004.ppt (PowerPoint presentation)

spam filter server side

Not all email clients provide sophisticated ways to filter emails.
In these cases it is possible to act upstream.

The “Authorized senders” feature allows you to receive messages
only from the senders you have previously authorized:

All the regular messages will arrive as usual in your inbox.
All the spam messages will go to a different mailbox.

No emails will be lost.
You may read the discarded messages mailbox once a day.
You will save so much precious time.