Microsoft Outlook is one of the most popular email clients in the world. Yet, despite its popularity, Outlook's integrated spam filtering doesn't catch much. As spammers use increasingly novel methods to skirt the default Outlook spam blocker, your inbox can come under attack from all manner of spam emails.

If your Outlook inbox is under spam siege, check out the top anti-spam tools for Outlook.

1. SpamBully

SpamBully takes the crown as the top-rated spam filter for Microsoft Outlook. It is a premium spam filter, but it delivers excellent results straight out of the box as it purges inboxes and keeps them clean.

SpamBully works with Office 365, Office 2019, Office 2016, and older Office versions.

SpamBully brings an extensive range of spam filtering and blocking to Outlook. It learns how you use your email, ensuring that only the good email passes to your inbox even as it removes spam automatically without you constantly updating your block list.

One of SpamBully's best features is the option to "punish" the spammer. You can return spam mail to the sender automatically, so it doesn't clog your inbox. It also reports the sender to the server it came from. The idea is to increase the cost of sending spam.

Another interesting feature is the email password for unfamiliar senders. If the address looks suspicious or spoofed, you can request the sender to enter a password before the email enters your inbox. A spammer isn't going to take the time to enter individual passwords for each spam email.

If you are unsure about a malicious email, why not try Google's phishing email quiz? It teaches you how to spot and avoid phishing emails and other malicious email types.

A one-year SpamBully subscription comes in at $29.95.

Download: SpamBully for Windows (Free Trial)

2. MailWasher Free and Pro

MailWasher is an Outlook spam filter that receives excellent reviews. MailWasher comes in two flavors: Free and Pro. The free version works with a single email account, but you cannot block incoming mail based on its country of origin or sync between the desktop and mobile versions of the app.

Those limitations aside, MailWasher Free offers many of the same features as the Premium version.

MailWasher uses an automated learning system to determine what is spam in your inbox and what it should leave intact. It has extensive filtering, which it uses in conjunction with customizable blacklists. The MailWasher interface is easy to use, allowing you to sort through spam emails rapidly. The auto-account detection works well, too.

A one-year MailWasher Pro license will set you back $49.95, and a lifetime license comes in at $100. MailWasher is also available for iOS and Android. However, you should note that the Mailwasher mobile apps aren't as highly rated as the desktop version, so keep that in mind.

Download: MailWasher Free for Windows | iOS | Android (Free)

3. SPAMfighter

spamfigher pro stats page

SPAMfighter is an award-winning free spam filter for Microsoft Outlook. SPAMfighter is a Microsoft Gold Partner, too, working closely to deliver a great spam filter.

Once installed, SPAMfighter protects all the accounts on your PC (including Outlook Express and Mozilla Thunderbird). When you receive an email, SPAMfighter checks it automatically. If it is spam, it heads straight to your spam folder.

If SPAMfighter misses a spam email, you can update the SPAMfighter definitions with a single click. The updated definition will eventually filter through to all other SPAMfighter users.

Handily, SPAMfighter creates whitelists automatically, and you can also filter emails using the language list.

Download: SPAMfighter for Windows (Free for Home users)

4. Spamihilator

spamihilator home page info

Spamihilator takes the prize for the best spam filter name. It isn't just an amusing name, though. Spamihilator is a useful free anti-spam tool for Outlook that will keep your inbox clear. Once installed, Spamihilator sits between Outlook and your network connection, catching spam before it hits your inbox.

Spamihilator is a great free spam-blocking tool. The Training Area feature lets you mark specific emails for future filtering, teaching the program to remove messages with similar content. Spamihilator becomes better the more you use the filters.

There is a setup wizard that appears automatically after installation. The wizard is fine if you have a POP3 email account. However, if you use IMAP, you must enter your email configuration within the Spamihilator settings.

If you are unsure about what email type you use, here are the differences between IMAP and POP3.

Unlike most other spam filters, Spamihilator offers a portable installer. A portable installer works directly from a USB flash drive, meaning you can use it to clean up spam on a different computer without installing it. You can find the portable installers on the Spamihilator download page.

Download: Spamihilator for Windows (Free)

5. Spam Reader

spam reader in outlook settings page

Spam Reader scans your inbox with impressive speed after installation. No sooner had I opened Outlook, Spam Reader reported back over 8,000 spam messages. It had scanned my existing spam box but also caught a lot of spam lurking in my inbox. Spam Reader nestles in your Outlook toolbar, as per the above image.

Aside from rapid scanning speed, Spam Reader tracks and analyses your inbox to understand your usage.

In this, it uses a "Good Email/Junk Email" method to deal with potential spam. Marking messages one or the other keeps false negatives from deletion before you have had a chance to check manually. Over time, Spam Reader learns that those false negatives should head straight to your inbox.

There are two Spam Reader versions: Free and Pro. The features are exactly the same. But after 30-days, the free version adds a small message to your outgoing emails. If that is not something you want, the Pro version comes in at $39.95 for a lifetime license with minor upgrades or $59.50 for a lifetime license with major upgrades.

Download: Spam Reader for Windows (Free)

What Is the Best Outlook Anti-Spam Software?

The default Outlook spam filter doesn't cut out enough spam. Spam is big business, and Microsoft is losing the war.

Spam varies between inboxes, of course. If your email has found its way onto a spam list, you will receive more spam than most. Data breaches are extremely common, unfortunately, so your email address could well be in the hands of the spammers.

Between these anti-spam tools for Outlook, you can't really go wrong with any option. The premium spam filters tend to work better than the free versions, as you might expect, but you can still filter and clean out your inbox with free spam-blocking software.