By default, email addresses in your Outlook contacts are considered safe senders by the Junk Email Filter. Email messages from safe senders are never moved to the Junk E-mail folder.
Note: If you use a Microsoft Exchange Server account, names and email addresses in the Global Address List (GAL) are also considered safe senders.
When you send a message to a person or organization that isn’t an Outlook contact, by default, the recipient email address isn’t added to the Safe Senders List. This means that when the recipient replies to your message, the reply message might be moved to the Junk E-Mail folder.
To make sure that your message recipients, even if they aren’t an Outlook contact, are on your Safe Senders List, do the following.
On the Home tab, in the Delete group, click Junk, and then click Junk E-mail Options.
On the Safe Senders tab, select the Automatically add people I e-mail to the Safe Senders List check box.