A safe sender is a contact who you consider safe to receive emails from that contain attachments (images, documents, etc.). Emails from these contacts will never be treated as junk email.
How to Add to Safe Senders list
Manage your junk email
At the top of the screen, select Settings > Mail.
Under Options, select Block or allow.
Under "Safe Senders and Recipients", click the edit button and add the address to mark as safe
A blocked sender is an email address that is treated as junk email. Emails from blocked senders follow the same rules as your Junk Mail. Messages from Blocked Senders are sent to your Junk Mail folder or deleted, depending on the Junk mail rules.
How to Block a mail sender
As part of its filtering criteria, the Outlook Junk Email Filter checks message senders against lists of email addresses and Internet domains designated either as safe or to be blocked. You can customize the filter to block or allow senders or different message types.
When you no longer want to see messages from someone, you can block a sender.
Right-click a message from the sender you want to block, and then click Junk > Block Sender.
The blocked person can still send you mail, but if anything from his or her email address makes it to your email account, it’s immediately moved to the Junk Email folder.
It’s a good idea to periodically review email messages identified as junk to make sure you’re not missing important messages.
If you later decide you want to unblock a sender, use Junk Email Filters to change which messages you see.