Why are blocked senders still getting through in Outlook?

You blocked a sender in Outlook, and their emails keep coming. Usually nothing is broken. The Blocked Senders list does less than most people expect: it moves mail to Junk instead of stopping it, it only matches exact addresses, and several other settings can override it. This guide walks through each cause, shows how to confirm which one applies using the message headers, and explains the admin-level block that works for a whole business.

Why are blocked senders still getting through in Outlook?

Blocked senders get through because Outlook's Blocked Senders list sorts mail rather than refusing it, and it only matches the exact From address or domain you entered. Microsoft's Block or unblock senders page says the junk filter "doesn't stop junk email from being delivered". A changed address, a Safe Senders entry or an unsupported account type are the other common causes.

Start with this table. Find the symptom that matches what you see.

Does blocking a sender in Outlook stop their emails?

No. Blocking a sender moves their future messages out of your Inbox. It doesn't stop the messages being delivered to your mailbox, and the sender gets no bounce. Microsoft says future messages from a blocked sender go to the Junk Email folder "or End-User Quarantine, if enabled by your administrator".

In Microsoft 365, the anti-spam policy decides which. Microsoft Learn says messages from your blocked senders get the header SFV:BLK and "are classified as spam". They're then delivered "to the user's Junk Email folder or to quarantine based on the action configured in the applicable anti-spam policy".

So if you see a blocked sender's messages in Junk, the block is working as designed. Junk Email is also cleaned automatically. Microsoft's help pages disagree on how fast: the Outlook.com missing-email page says messages are removed from Junk after 30 days, while the blocked-senders page (for new Outlook, Outlook on the web and Outlook.com) says 14 days. Either way, don't rely on Junk to keep anything. In a Microsoft 365 work account, how long Junk keeps mail depends on your organization's retention settings.

Why does the same spammer keep getting past my block?

Because the block only matches what you entered, and spammers change it. Blocked Senders accepts an exact email address such as offers@example.com or a whole domain such as example.com. A campaign sent from offers@example2.com the next day doesn't match either.

Microsoft is explicit about what's compared. Its blocklist guidance says Outlook Blocked Senders "use the From address", the address shown in your email client (also called the 5322.From address). It doesn't match:

• The display name. Blocking "Microsoft Support" <x@bad.example> does nothing for "Microsoft Support" <y@other.example>. Our display name spoofing guide explains why scammers rely on this.
• The envelope sender (the 5321.MailFrom or Return-Path address), which can differ from the From address.
• Words in the subject or body. Blocked Senders isn't a keyword filter.

What to do instead:

1. Block the domain, not the address, if the sender uses many addresses at one domain and you never need mail from it. Don't block shared consumer domains such as gmail.com or outlook.com, or you'll block everyone who uses them.
2. Report the message with Report > Report junk or Report phishing. Microsoft's blocklist guidance says reported sources that prove harmful can be blocked automatically, without you maintaining a list.
3. Ask IT for a filter-level fix if the spam rotates domains daily. That's a filtering problem, not a list problem. Our guide to why you get so much spam explains where it comes from.

If the spam looks like it comes from your own address, don't block yourself. Read someone is sending email from my address instead.

Can Safe Senders override Blocked Senders?

Yes. If the same address or domain is on both lists, Safe Senders wins. Microsoft's order of precedence page says: "If the same email address or domain exists in a user's Safe Senders list and Blocked Senders list, the Safe Senders list takes precedence."

This catches people out in three ways:

• You added the sender to Safe Senders months ago and forgot.
• You saved them as a contact and Trust email from my contacts is on. Microsoft counts trusted contacts alongside Safe Senders, so the contact entry can behave like a safe sender.
• Classic Outlook added them automatically through Automatically add people I email to the Safe Senders list, after you replied to them once.

Check all three places, remove the sender, then keep the block. In new Outlook and Outlook on the web, both lists are under Settings > Mail > Junk email. In classic Outlook, go to Home > Block > Junk E-mail Options, then the Safe Senders and Blocked Senders tabs. Our Outlook junk email filter settings guide explains every option on those tabs.

What about organization settings?

Admin settings and your personal list interact, and Microsoft documents who wins. The pattern for Blocked Senders is mostly reassuring:

So an admin allow doesn't normally break your block. The exception is the advanced delivery policy, used for security team mailboxes and phishing simulation tests. If you're on a security team and blocked a simulation sender, that's why it still arrives.

Why can't I block certain senders at all?

Some senders can't be blocked from your own list because of how the account or directory works. Microsoft's support page lists two cases.

• People in your organization. In classic Outlook, entries in your organization's Global Address List "are automatically considered safe and can't be added to the blocked list". A coworker or an internal distribution list can't be blocked by you. That's a conversation for your manager, IT or HR.
• Third-party accounts in new Outlook. Microsoft says new Outlook doesn't block senders for accounts such as Gmail or Yahoo. Block them in that provider's settings instead.

A third, less common case is list size. Microsoft Learn says the whole safelist collection (Safe Senders, Safe Recipients and Blocked Senders together) has a 510 KB limit. Past it, Outlook shows "You are over the size allowed on the server" and "The Junk E-mail filter on the server is disabled" until you shrink the lists. The support page also says you can have up to 10,000 addresses or domains across the blocked and safe senders lists.

For Microsoft 365 mailboxes there's a subtler limit: Microsoft says only the first 500 blocked sender entries have their hashes synced to Microsoft Entra ID. Messages from senders beyond that point don't get a "User Block" verdict. Microsoft says that unless they're otherwise detected as malicious, they're delivered to Junk Email instead of quarantine, and if they are quarantined, quarantine notifications are sent for them. Two near-identical spam messages can be handled differently depending on where each sender sits in your list.

Do Outlook blocks work on my phone and other devices?

For Microsoft 365 and Exchange Online mailboxes, yes, because the block lives in the mailbox, not in one app. Microsoft Learn says the safelist collection "is saved in the Exchange Online mailbox so that the changes to the safelist collection in Outlook appear in Outlook on the web, and vice-versa". The server sorts the message into Junk Email before any app downloads it, so the phone app shows it in Junk too.

Two situations look like a broken block but aren't:

• A notification arrived before you noticed the message was in Junk. Check which folder the message is actually in before assuming the block failed.
• You blocked the sender in a phone's built-in mail app. A block set in a device's own app may not be written back to your mailbox's Blocked Senders list. Add the block in Outlook on the web or new Outlook instead, so it applies everywhere.

If you use several accounts in one Outlook app, check you added the block to the right account. Each mailbox has its own lists.

How do I check whether a block worked on a specific message?

Read the message's anti-spam header. Microsoft 365 records the result in the X-Forefront-Antispam-Report header, and three values tell you what happened:

• SFV:BLK: "the message was blocked because it was sent from an address in a user's Blocked Senders list". Your block matched.
• SFV:SFE: the message "was allowed because it was sent from an address in a user's Safe Senders list". A safe entry beat the block.
• SFV:NSPM or SFV:SPM with no BLK: the block didn't match this message's From address.

To view headers in Outlook on the web, Outlook.com or new Outlook, select More actions (...) on the message, then View > View message details. In classic Outlook, open the message and select File > Properties. Here's a shortened example (placeholder values):

X-Forefront-Antispam-Report: CIP:198.51.100.20;CTRY:;LANG:en;SCL:5;
  SRV:;IPV:NLI;SFV:BLK;H:mail.offers.example;DIR:INB;CAT:SPM;
From: "Weekly Deals" <deals@offers.example>

Paste a full header into our Microsoft 365 Spam Header Decoder to decode every field, or see Microsoft 365 spam headers explained.

How do admins block a sender for everyone?

Use the Tenant Allow/Block List. Microsoft ranks it first of its blocking methods, ahead of each user's Blocked Senders list. Messages from blocked entries are marked high confidence spam, and Microsoft notes a bonus: users in your organization also can't send email to a blocked domain or address. They get the bounce 550 5.7.703.

In the Microsoft Defender portal, go to Email & collaboration > Policies & rules > Threat policies > Tenant Allow/Block Lists, open the Domains & addresses tab, select Add, then Block. Our guide to blocking a sender or domain in Microsoft 365 has the full steps, PowerShell and entry limits.

Admins can also inspect or clean up a user's own lists in Exchange Online PowerShell:

(Get-MailboxJunkEmailConfiguration -Identity "ori@example.com").BlockedSendersAndDomains
(Get-MailboxJunkEmailConfiguration -Identity "ori@example.com").TrustedSendersAndDomains
Set-MailboxJunkEmailConfiguration "ori@example.com" -TrustedSendersAndDomains @{Remove="deals@offers.example"}

The @{Remove=...} syntax removes one entry without wiping the rest of the list. Microsoft also notes that the Enabled parameter on that cmdlet "has no effect on mail flow in cloud mailboxes", so switching the junk rule off and on is not a fix. Worse, its cmdlet reference says that with -Enabled $false "the safelist collection of the mailbox is unable to move delivered messages between the Inbox or the Junk Email folder," so leave it at the default, $true.

If the senders you need to stop change every day, lists won't keep up. Blocking before mail reaches Microsoft 365 with a filtering gateway's own allow and block lists and spam filtering is the next step for many small businesses.

Next steps

• Check Safe Senders, contacts and Blocked Senders for the same address, and remove the conflict.
• Look for SFV:BLK in the headers of the next message that gets through, to see whether the block matched.
• Report persistent spam rather than adding a new block for every address.
• Admins: move recurring blocks into the Tenant Allow/Block List, and review why Microsoft 365 spam gets through.
• If list-based blocking can't keep up, see how iBlockSpam's allow and block lists and filtering work in front of your mailboxes.