What a mailbox actually costs
A monthly price only tells you what one mailbox costs. We divided four real prices by 1, 3, 5, 10 and 15 mailboxes to see what changes.
Every pricing page opens with one number. €4.95 a month. $8 a month. €3.99 a month. It is the easiest thing to compare, and it is also the least useful, because almost nobody buying a spam filter for a domain is buying it for one mailbox.
So we took the four products in our own comparison that publish a real, checkable price, and divided each one by 1, 3, 5, 10 and 15 mailboxes. What came out the other side was mostly what you would expect. A couple of things were not.
Four prices that get cheaper the more you use them
Klar Plus is licensed per person, with unlimited inboxes and Macs. SpamHero, EuropeanMX and Clean Mailbox are all sold per domain, filtering mail at the MX record before it reaches any mailbox behind it. None of the four has a technical way to charge per mailbox even if it wanted to, so the arithmetic is simple: the same price, divided by a growing number, falls every time you add a mailbox. A per-seat tool does the opposite. Add a mailbox and the bill moves with it.
That is the whole idea, and it is not ours. A recent comparison of multi-account email clients ran the same division across a different set of products and reached the same conclusion: a flat price gets more generous with scale, a per-seat price never does. Worth borrowing, applied honestly to our own market instead of copied wholesale.
What the fine print actually says
We are not going to pretend every one of these numbers was exactly what its own pricing page led with. Checking each vendor's terms directly turned up three things worth knowing before you compare anyone on price alone.
- SpamHero's cheapest advertised rate needs a full year prepaid upfront and quietly renews higher after that. We used its ordinary month-to-month rate instead, the same way every other product here is priced.
- EuropeanMX's number excludes VAT and requires paying for a year at once. It is the only one of the four that assumes a yearly commitment; the other three are cancel-anytime.
- SpamHero and Clean Mailbox both meter the mail a domain receives, not its mailbox count. Send more mail than the tier allows and the price in this chart stops being the whole story.
None of that changes which direction the four lines point. It changes what a specific number means, which is exactly the kind of thing a headline price never tells you either.
Cost per mailbox
Monthly cost per mailbox, in euros, at 1, 3, 5, 10 and 15 mailboxes on one plan.
- Klar Plus · per person, unlimited mailboxes
- SpamHero · per domain, unlimited mailboxes
- EuropeanMX · per domain, up to 100 mailboxes
- Clean Mailbox · per domain, unlimited mailboxes
- Free · Klar's free app, and open-source filters
Klar Plus is not on sale yet. €3.99/month is the launch price we intend to charge, not a price you can buy today; it rises once the launch window ends, the same as everywhere else this figure appears on the site.
SpamHero, EuropeanMX and Clean Mailbox filter mail at the domain's MX records, before it reaches any mailbox on that domain. That is why the price does not vary with mailbox count within a plan: MX filtering has no technical need to meter mailboxes. A vendor can still cap how many a plan covers by contract, as EuropeanMX does at 100 per domain on this tier; SpamHero and Clean Mailbox state no such cap.
SpamHero (25,000 inbound messages a month on this tier, additional capacity at $5/month per 100,000) and Clean Mailbox (6,000 inbound messages a month on this tier, then delivered unfiltered for free or filtered at an extra per-message rate, depending on the plan) both meter the mail a domain receives, not its mailbox count. A domain that receives more mail than its tier allows can end up paying more, or losing filtering on the overflow.
EuropeanMX's €4.95 excludes VAT and requires billing annually upfront, same as the price column above. Every other figure in this chart is a no-commitment rate, billed month to month, so EuropeanMX's is the one number here that assumes a yearly commitment in exchange for its price.
Klar Plus, EuropeanMX and Clean Mailbox already bill in EUR. SpamHero's $8/month converts to a whole euro here, at the same rate /pricing uses, so this chart never disagrees with that page.
Where you probably sit
How many mailboxes are you actually running?
Pick your scale
The gap between these prices barely exists at one mailbox and gets hard to ignore by fifteen.
Choose roughly where you land.
Every option looks close.
At one mailbox, all four priced products here sit within a few euros of each other. The difference barely matters yet.
What we would not put a number on
Two other products in our comparison are also genuinely tiered by account count, and we looked into both before deciding not to plot them. One publishes its tier structure but renders a placeholder price through client-side scripting that never resolved to a real figure. The other has real pricing tiers, almost certainly, but the only page that could confirm the exact numbers would not load, and two secondhand sources that claimed to know disagreed with each other. A chart is only as honest as its worst number, so both stayed off it. They are still in the full comparison table, named plainly for what they are.
The rest of what we found, cell by cell, source by source, is in the chart above rather than repeated here. Divide your own mailbox count into it and see where you land.
