Keeping spam out

Every mailbox on the server is filtered, from the moment it is created, without anybody switching anything on. This page is about the three things you can change when the default is not quite right for you: how hard the filter looks, what i

Written for: Customer, Reseller, Administrator

Where to find it — Panel → Hosting → Accounts → your account → Mail → click the mailbox → the Spam tab.

What happens by default

Every new mailbox starts the same way:

the filter is on;
it acts at 6 points — the score the filter gives a message, where higher means more suspicious;
and what it does is move the message to the Junk folder.

Nothing is deleted and nothing is refused. That is on purpose: you can always look in Junk and drag a message back, and you cannot get back a message that was thrown away.

Making it stricter or looser

The Sensitivity slider is the only number worth touching. Slide it towards Stricter and the filter catches more spam — and holds back more ordinary mail along with it. Slide it towards Looser and the opposite happens.

If you are not sure, leave it. The default works for almost everybody, and the two lists further down this page are a much better answer to "the filter is wrong about this one sender".

What happens to the mail it catches

Three choices, under What happens to it:

Move it to Junk (the default). The message is delivered, marked, and filed in your Junk folder. You can still find it, and dragging it back out teaches the filter it was wrong.

Delete it straight away. The message is dropped and there is nothing left to recover. Only choose this for an address that gets nothing but spam.

Refuse it at the door. The message is never accepted, and the sender gets told it did not arrive. That is honest — a real sender knows their mail did not reach you — but a false positive here means somebody thinks you are unreachable.

Senders that must always get through

Under Senders you can name up to 200 addresses or domains that are always allowed or always blocked, whatever the filter thinks of them:

Always allow — a customer whose newsletters keep being filed as spam, or an accountant whose mail server has an old configuration.
Always block — a sender that keeps getting through and that you never want to hear from.

You can name a full address (someone@example.com) or a whole domain (example.com), and a domain covers every address at it.

An allowed sender always wins over the sensitivity. However strict you set the slider, mail from a sender on your allow list arrives in your inbox. That is not a matter of which setting happens to be applied first — an allowed sender is worth so much less than any threshold you can choose that the question does not arise.

A blocked sender is refused at the door with an error the sender can read, even if the rest of your settings would only have filed the message in Junk.

One address is on one list. Putting a sender on the block list when it is already on the allow list moves it, rather than leaving you with two rules that disagree.

Teaching the filter

The filter learns from what people actually do, and there is no button for it.

Drag a message into Junk and the filter learns that mail like it is spam.
Drag a message out of Junk and it learns the opposite.

Do that a handful of times and it starts getting your mail right on its own. The learning is shared by everybody on the server, so it is worth doing.

Testing that it works

There is a standard test message every spam filter in the world recognises. Send yourself a message whose body is exactly this line and nothing else:

XJS*C4JDBQADN1.NSBN3*2IDNEN*GTUBE-STANDARD-ANTI-UBE-TEST-EMAIL*C.34X

With the default settings it arrives in your Junk folder — not bounced, because you chose "move it to Junk". If you set the mailbox to Refuse it at the door first, the same message is refused instead. Either way, you have just seen your own settings working.

From the command line

Everything on this page is also a command, if you have shell access to the server:

corectl mailbox spam show info@example.com
corectl mailbox spam set info@example.com --threshold 8
corectl mailbox spam set info@example.com --action junk
corectl mailbox spam set info@example.com --reset

corectl mailbox senders add info@example.com klant@voorbeeld.nl --kind allow
corectl mailbox senders add info@example.com casino.example --kind block
corectl mailbox senders list info@example.com
corectl mailbox senders remove info@example.com casino.example

How much mail you may send

There is a ceiling on outgoing mail, and it is there to protect you: a website with a security hole sends thousands of messages before anybody notices, and what it costs is not those messages — it is the whole server ending up on a blocklist, so that your mail stops arriving anywhere.

By default a mailbox may send 100 messages an hour, an account 500, and a whole server 2500. Mail over the limit is not refused: it is held and delivered later, and your mail program retries by itself. You will normally not notice.

If you legitimately need more — a newsletter, a busy webshop — ask your hosting provider; the limit is adjustable per account.

Mail your website sends with PHP counts against the same limit as mail you send from your mail program. That is deliberate: it is exactly the traffic a compromised site produces.