Outlook and Microsoft 365 allow-list
Outlook whitelist-only mode: block all email except contacts.
Outlook has no single “contacts only” switch, but four built-in options come close: Sender Screening for personal Outlook.com accounts, the safe-senders-only junk setting (Safe Lists Only in classic Outlook), a classic Outlook rule that skips your Contacts address book, and admin mail flow rules in Microsoft 365. KeepKnown does it for Outlook and Microsoft 365 without sending anyone to Junk.
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Outlook does not have one identical whitelist-only switch across every product. Outlook.com, Outlook on the web, new Outlook, classic Outlook, and organization-managed Microsoft 365 mailboxes expose different combinations of Safe senders, trusted contacts, junk settings, rules, and administrator controls. Microsoft's junk email settings guide describes the option that treats mail as junk unless the sender is on your safe list.
Microsoft also documents that contacts can be treated as safe senders in supported Outlook versions, and its Safe Senders guidance explains differences for Exchange and Exchange Online. Confirm the account type before applying a strict workflow.
KeepKnown adds a separate relationship-based layer: contacts, approved domains, and people you have replied to stay in the inbox, while everyone else moves out of the inbox with a KK:OUTSIDERS category. The message is not blocked, deleted, or mixed in with Junk.
Short answer
Pick the option that matches your Outlook account.
Personal Outlook.com: turn on Sender Screening. Any Outlook: add trusted senders to Safe senders and only trust your safe lists, which sends everyone else to Junk. Microsoft 365 admins: use a mail flow rule. Use KeepKnown to keep unknown senders apart from spam and easy to review.
Outlook.com personal accounts: Sender Screening
- Open Settings, select Account, choose your personal Microsoft account, then select Sender Screening and turn it on.
- Mail from unscreened senders is grouped at the top of your inbox.
- Open the group and mark each new sender as allowed or blocked.
- Allowed and blocked senders sync with the Safe and Blocked senders lists in Outlook on the web.
Outlook.com and Outlook on the web: safe senders only
- Open Settings, select Mail, then Junk email, and add the people and domains you trust under Safe senders and domains.
- Keep Trust email from my contacts turned on so saved contacts count as safe senders.
- Turn on the option to only trust email from your Safe senders list. The exact wording varies by Outlook version.
- Save, then check the Junk Email folder for a few days to catch real senders you forgot to add.
Classic Outlook for Windows: Safe Lists Only
- On the Home tab, select Junk, then Junk E-mail Options.
- On the Safe Senders tab, add trusted addresses or domains and tick Also trust e-mail from my Contacts.
- On the Options tab, choose Safe Lists Only and select OK.
- Review the Junk E-mail folder regularly. Anything not on your lists lands there.
Classic Outlook: move mail from anyone not in Contacts
- On the Home tab, select Rules, then Manage Rules & Alerts, then New Rule.
- Start from a blank rule that applies to messages you receive.
- Skip the conditions, choose move it to the specified folder, and pick a folder such as Not in contacts.
- Add the exception except if sender is in specified Address Book and choose Contacts.
- Finish the rule. It is a client-only rule, so it runs only while classic Outlook is open on your computer.
Microsoft 365 admins: a mail flow rule
- Open the Exchange admin center and go to Mail flow, then Rules.
- Create a rule that applies when the sender is outside the organization.
- Add exceptions for approved sender addresses or domains, and target only the mailboxes that need strict screening.
- Choose an action such as delivering to hosted quarantine or marking the message as spam, then test it on one mailbox first.
Outlook allow-list controls by environment
| Environment | Native controls to check | Important caveat |
|---|---|---|
| Outlook.com | Safe senders and domains, blocked senders, inbox rules | Safe senders prevent trusted mail from being treated as junk |
| New Outlook for Windows | Safe senders, blocked senders, rules | Available controls depend on the connected account type |
| Classic Outlook | Junk Email Options, contacts, Safe Senders, Safe Lists Only | Exchange Online may apply server-side filtering separately |
| Managed Microsoft 365 | Inbox rules plus organization policies and mail-flow controls | Coordinate with the administrator before strict enforcement |
Safe-senders-only mode vs KeepKnown
| Question | Outlook safe lists only | KeepKnown |
|---|---|---|
| Who reaches the inbox | Safe senders, safe recipients, and optionally contacts | Contacts, VIP domains, and people you have replied to |
| Where everyone else goes | Junk Email folder, alongside real spam | Out of the inbox with a KK:OUTSIDERS category |
| Keeping the list current | Add each new sender by hand | Follows your contacts and replies |
| Where it applies | Depends on the Outlook version and admin policy | The mailbox itself, so every Outlook app sees the result |
| Preview before turning it on | Not available | Preview recent matches, then activate |
A recoverable approved-sender workflow
Connect Outlook
Authorize KeepKnown with Microsoft so it can apply contact-based screening.
Confirm trusted senders
Use contacts, approved domains, prior correspondents, and VIP groups for people who should reach the inbox.
Screen everyone else
Preview the matches, save the filter paused, then route unfamiliar senders to a review area when it is ready.
Questions before you connect.
Can Outlook only allow emails from contacts?
Approximately. Keep contacts trusted as safe senders and turn on the option to only trust your safe lists (Safe Lists Only in classic Outlook); mail from everyone else goes to Junk. Personal Outlook.com accounts can also use Sender Screening.
How do I block all emails except contacts in Outlook?
Use the safe-senders-only junk setting, or in classic Outlook create a rule that moves messages except if the sender is in your Contacts address book. Microsoft 365 admins can use a mail flow rule with approved-sender exceptions.
What is Sender Screening in Outlook?
A setting for personal Outlook.com accounts that groups mail from senders who are not on your allowed or blocked lists at the top of the inbox, so you can allow or block each one.
How do I whitelist an email address in Outlook?
Open Settings, select Mail, then Junk email, and add the address or domain under Safe senders and domains. In classic Outlook use Junk, Junk E-mail Options, then the Safe Senders tab.
Can Outlook run in whitelist-only mode?
Some Outlook environments support strict junk-mail settings, trusted contacts, Safe Senders, or administrator policies. The exact controls depend on the account type and Outlook version.
Does KeepKnown support Outlook and Microsoft 365?
Yes. KeepKnown supports Outlook and Microsoft 365 inboxes connected with Microsoft authorization.
What happens to non-approved Outlook senders?
With Outlook's own setting they go to Junk. With KeepKnown they move out of the inbox with a KK:OUTSIDERS category instead of being permanently blocked or deleted.
Are Outlook contacts automatically safe senders?
In supported Outlook versions, contacts can be treated as safe senders. Behavior can differ for Exchange and organization-managed accounts, so confirm the mailbox and policy configuration.
Outlook allow-list
Route non-approved senders without permanent blocking.