How Spam Filtering Works, and Auto-Deleting Spam Print

How we filter your spam

Every message arriving at your domain is checked by SpamAssassin, the spam filter running on our servers. It scores each message on how spam-like it looks, the more suspicious the signals, the higher the score, and acts based on that score. This runs automatically on all mail, with nothing for you to switch on.

What we do by default: tag, not delete

By default, we do not delete anything the filter suspects. Instead, when a message scores at or above our spam threshold, we prepend its subject line with ***SPAM***, so it still arrives in your inbox, but clearly flagged as something our filter judged to be spam.

This is a deliberate choice, and an important one. Tagging rather than deleting means you never silently lose a message. The filter is good, but no spam filter is perfect, and occasionally a real message, a newsletter you wanted, an unusual but genuine email, scores high enough to look like spam. By tagging it instead of binning it, we make sure that message still reaches you, marked for your attention rather than vanished without a trace. You stay in control of what is really spam and what is not.

Using the tag to sort your mail

The * SPAM * tag becomes genuinely useful when you pair it with a filter. Because every suspected spam message has that consistent tag in its subject, you can create a simple email filter that moves anything containing * SPAM * into a dedicated Spam or Junk folder automatically, keeping your inbox clean while still keeping the suspected spam where you can review it. Our article on email filters walks through creating exactly this kind of rule. This is the setup we would recommend for most people: filtered out of sight, but still there to check.

If you want spam deleted automatically

Some people genuinely do not want to see spam at all, not even in a folder. If that is you, we can set your account to automatically delete messages that meet the spam threshold, rather than tagging them. Just ask us and we will switch it on for your account, at the same threshold we use for tagging.

Understand the trade-off before you ask for this, because it is a real one. Auto-deleted spam is gone, silently and permanently, with no folder to check and no way to recover it. If a genuine message ever scores as spam, and occasionally one will, auto-delete means you will never know it existed. That is the price of never seeing spam: you also never see the rare real message caught alongside it. For this reason we do not turn auto-delete on by default, and for most people the tag-and-filter approach above is the wiser choice, all the tidiness, none of the silent loss. Choose auto-delete only if you genuinely accept that trade.

When good mail gets tagged, or spam gets through

No filter is perfect, and two things will happen occasionally:

• A real message gets tagged as spam. This is exactly why we tag rather than delete, the message still reaches you. If it happens often with a particular sender, that is worth a support ticket so we can look at why.
• Some spam slips through untagged. No filter catches everything. A persistent spam problem is also worth raising with us.

If your spam problem is heavy and the standard filtering is not keeping up, there are stronger commercial filtering options available as an add-on, which we can tell you about, our article on stronger email spam filtering covers what is possible beyond the built-in filter.

Good to know

The safest, tidiest spam setup for most people is the one that hides spam without ever destroying it: let our filter tag suspected spam, add a filter that moves the tagged mail into a Spam folder, and glance at that folder occasionally to catch the rare real message that landed there. That gives you a clean inbox and a safety net at the same time. Auto-deletion removes the safety net, so keep it for cases where you genuinely never want to see spam and accept the small risk that comes with that. When in doubt, tag and filter rather than delete, mail you can still find beats mail that is silently gone.