Business spam filter for Microsoft 365, Google Workspace & cPanel
Spam stops at your domain. Business mail gets through.
iBlockSpam filters every message for your whole domain before it reaches Microsoft 365, Google Workspace or your own server. Each person reviews their own quarantine. You pay per domain, not per mailbox.
Illustration. Senders and subjects are examples.
Works alongside Exchange Online Protection. Setup uses a restricted inbound Partner connector with Enhanced Filtering for Connectors, so Microsoft still sees the original sender's IP address.
Add our servers as an inbound gateway in the Admin console, then point your MX records to iBlockSpam. Test with real messages before you lock down direct delivery.
Point MX to iBlockSpam and set the domain's mail routing so your server still accepts and delivers locally. We'll help you check aliases, forwarders and catch-all addresses.
The idea in 15 seconds.
One filter in front of your whole domain: junk is held back, real mail goes straight through.
See the portal.
This is what you get after the switch: every domain's status, mail delivered and held, Domain Watch, lookalike domains, DMARC monitoring and a setup checklist. Click through it with sample data, no sign-up needed.
What gets checked before a message reaches anyone.
A phishing email looks ordinary in an inbox. In its headers, it gives itself away. Scroll through the checks.
Return-Path: <bounce@mailer-xq7.example>Received: from mailer-xq7.example ([203.0.113.77])From: "Microsoft 365 Billing" <billing@micros0ft-billing.example>Reply-To: payments-desk@freemail.exampleSubject: Payment failed — update your card todayAuthentication-Results: spf=fail; dkim=none; dmarc=failLink: https://micros0ft-billing.example/loginAttachment: invoice_0921.html
Illustrative message using reserved example domains.
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1
Look-alike sender
The display name says Microsoft. The domain is micros0ft-billing — a zero where the o should be. Impersonation checks compare senders against the names people trust.
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Replies go somewhere else
Reply-To points at a free mailbox, not the sender. Answering would hand your reply straight to the attacker.
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It fails authentication
SPF fails, there is no DKIM signature and DMARC fails for the From domain. A real Microsoft message passes all three.
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The link leads to a fake login page
The link uses the same look-alike domain as the sender. Link and sender reputation are checked before delivery, not after a click.
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An HTML attachment
An .html "invoice" is a common way to open a fake sign-in form offline. Attachment-type filters can hold these on arrival.
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Held in quarantine
The message never reaches the inbox. It waits in quarantine, where the right person can review it — and release it if it was legitimate after all.
We checked the world's 1,000 busiest websites.
Even the biggest names leave gaps that let attackers send mail in their name. We ran our Email Health Check engine against the Tranco top 1,000 domains on October 9, 2026.
don't enforce DMARC — so receivers aren't told to reject mail that spoofs them.
DMARC policy of the top 1,000
Only quarantine and reject actually stop spoofed mail.
Enforcement by popularity
Share with DMARC at quarantine or reject.
How many DNS lookups their SPF needs
Limit: 10 — above it, SPF breaks22 sites exceed the limit, so receivers treat their SPF as failed.
Newer protections are still rare
Share of sites that publish each record.
Source: iBlockSpam analysis of the Tranco list PY35J (2026-10-08), 1,000 domains, public DNS. Full methodology and data
What 30 days of filtering looks like.
Real, anonymized traffic from business domains on our filtering service. Every column is one day — and roughly one message in six never needed to reach an inbox.
- Messages filtered
- 74,147
- Held as spam or threats
- 18%
Anonymized daily totals across 6 business domains filtered by the iBlockSpam service, 2026-09-19 to 2026-10-18. "Held" includes spam, phishing and malware. Full methodology and data
Switching without losing a message.
Every step is checked before the next one starts, and every screen shows how to undo it.
How the setup works-
1
Check
Run a free check on your domain. We read your MX, SPF and DMARC records, show where your mail goes today, and flag problems worth fixing before you change anything.
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Configure
The setup wizard walks you through your platform's steps, such as a Microsoft 365 inbound connector or a Google Workspace inbound gateway, then the MX change. You see your DNS before and after, plus the rollback steps.
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Verify
Send a test message and confirm it passed through filtering and arrived in the right mailbox. We don't call a domain protected until mail is actually flowing through it.
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Monitor
We keep watching your MX, SPF and DMARC records and alert you if they change unexpectedly: weekly on Protect, daily on Protect Plus.
Free tools that show their work.
Each result shows the record we read and when. Checks that couldn't run say so — they never count as failures.
One price per domain.
Ten people or two hundred, the price stays the same. Every user gets a personal quarantine, and outbound relay is included.
Protect plan, billed annually. $15 month to month. Beta pricing in USD. 30-day money-back guarantee on your first annual plan.
- Unlimited mailboxes
- Personal quarantine for everyone
- 100,000 inbound messages a month
- 500 outbound relay messages
- Mail held up to 5 days if your server is down
- 30-day message history
The honest answers to the usual worries.
What people ask before they put a filter in front of their business mail.
Will real email get blocked?
Suspicious messages are held in quarantine, not deleted. Each person has a personal quarantine and gets a digest email on the schedule they choose (hourly, daily, on a set weekday or custom), and they can release a message that was held by mistake. Admins also get a domain-wide shared quarantine, approved-sender lists keep known contacts flowing, and 30 days of message history let you trace what happened to any message. How quarantine works.
Isn't Microsoft 365 or Google Workspace filtering enough?
For some organizations it is, and iBlockSpam works alongside it rather than replacing it. A gateway adds an independent layer in front of the mailbox: personal quarantines with digests, sender verification on approved lists, geographic, attachment-type and Office macro filters, and up to 5 days of outage spooling. Our comparisons set out what each option does: Microsoft 365 built-in vs a gateway and Google Workspace built-in vs a gateway.
Where is our email processed?
Mail is processed in the United States, and message history is kept for 30 days. Our security page explains what passes through filtering, what we store and who can see a quarantine. The subprocessor list shows who helps us run the service.
What if your service goes down?
Email is built to ride out short outages: a sending server that can't connect keeps retrying, usually for several days, before it gives up, so an interruption delays mail rather than losing it. On your side, if your own mail server is unreachable, we hold incoming mail for up to 5 days and deliver it when the server is back. See outage spooling.
Who do I talk to when something's wrong?
A person. Email support@iblockspam.com or use the support page, and someone reads every message. If mail has stopped arriving, say so in the subject line so it's seen straight away. Protect Plus also includes a human setup session for your cutover.
Still deciding?
A domain's first annual subscription has a 30-day money-back guarantee, and you can start with a free check of your current setup.
Small businesses
One price per domain covers every mailbox, so adding a new starter doesn't add a line to your bill. Guided setup means you don't need an email specialist on staff.
Read moreMSPs
Protect client domains on mixed platforms from one place, with per-domain costs you can predict and quarantines your clients' users can manage themselves.
Read moreHosting providers
Offer inbound filtering on the domains you already host, including cPanel servers. Partner terms, including pricing, are agreed individually.
Read moreLearn how email security really works.
Plain-English guides with primary sources: RFCs, Microsoft Learn and Google's own documentation.
What is DMARC, and how does it work?
What DMARC is, how it uses SPF and DKIM alignment, what p=none, quarantine and reject do, what the reports show, and how to set it up in five safe steps.
9 min read Running email day to dayWhy is spam getting through the Microsoft 365 spam filter, and how do you fix it?
Why spam reaches Microsoft 365 inboxes: allow lists, SCL -1 rules, weak policies, Direct Send. How to find the cause in headers and fix it step by step.
9 min read Running email day to dayEmail deliverability checklist: how to reach the inbox in 2026
A sender checklist for reaching the inbox in 2026: aligned SPF, DKIM and DMARC, reverse DNS, TLS, one-click unsubscribe, spam rates, warming and monitoring.
9 min read SPF, DKIM & DMARCHow to stop others sending email as your domain
Stop criminals sending email as your domain: the DMARC path to p=reject, SPF and DKIM, subdomains and parked domains, monitoring, and what DMARC can't stop.
9 min read SPF, DKIM & DMARCWhy does DMARC fail? Causes and fixes for dmarc=fail
Troubleshoot dmarc=fail: alignment vs pass, third-party senders, forwarding, subdomains, DKIM d= and SPF MAIL FROM mismatches, with a causes-to-fixes table.
9 min read Phishing & threatsAI phishing emails: what has changed and what still stops them
How generative AI changes phishing, from flawless grammar to cloned voices, according to the FBI and NCSC, and which defenses still stop AI-written attacks.
9 min readQuestions before you switch.
More on the FAQ page, or ask a person.
Will iBlockSpam work with our email provider?
Yes, if your mail server can receive mail from a filtering gateway. We have guided setups for Microsoft 365, Google Workspace and cPanel/WHM, and we also deliver to Exchange and other standard SMTP servers. Each platform needs its own steps, such as an inbound connector in Microsoft 365 or an inbound gateway in Google Workspace. Run the free health check first to see where your mail goes today.
What happens if mail stops arriving?
First, nothing is lost just because your own server is down: we hold mail for up to 5 days and deliver it when the server is back. If mail stops for another reason, contact support with your domain and the time it started. Your setup record keeps your previous MX values, so rolling back is a DNS change you can make straight away.
Can we leave safely if it isn't right for us?
Yes. Leaving is a DNS change. Before your service ends, we help you point your MX records back to your previous provider (or a new one) so mail keeps arriving, and you undo the platform settings we helped you add. Your setup record lists your original DNS values to make the switch straightforward.
Does changing our MX records affect mail we already have?
No. MX records only control where new incoming mail is delivered. Mail already in your mailboxes, your folders, calendars and contacts stay exactly where they are. During DNS propagation some senders will use the old route and some the new one for a while, which is why we ask you to keep both working until the change has settled.
What's the difference between the mailbox and message limits?
Pricing is per domain, so you can protect as many mailboxes and domain aliases as you need. That covers how many mailboxes, not how much mail. Each domain includes 100,000 inbound messages per month, and individual messages can be up to 400 MB. If you expect more than that, talk to us before you sign up so we can plan for it.
Do you filter outgoing email too?
You can send through our outbound relay (smart host). It signs messages with DKIM and filters outbound mail, which helps catch a compromised account sending spam in your name. Both plans include 500 outbound relay messages per domain per month. Using the relay is optional; inbound filtering works without it.
How is pricing calculated?
You pay per protected domain, not per user. Protect is $12 per domain per month billed annually ($144 a year) or $15 month to month. Protect Plus is $19 billed annually ($228 a year) or $24 month to month. These are beta prices in USD, excluding tax. For MSPs and hosting providers, partner terms, including pricing, are agreed individually.
See what your domain lets through.
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