A spam filter is the mechanism by which a mail service like Gmail or Outlook decides whether an email deserves the inbox or the junk folder. That sorting happens in a fraction of a second, before the recipient even sees the message. Understanding its logic helps you write email that actually arrives.
What the filter watches
The filter does not read an email the way a person does. It adds up signals and computes a score. The first of these is sender reputation: do your domain and your address have a habit of sending messages that are well received? A fresh address, or one tied to complaints, starts with a handicap.
Next comes technical authentication, which proves you really are the sender you claim to be, then the content itself. A message crammed with capitals, exaggerated promises or shady links looks like mass advertising. Finally, recipient behaviour weighs heavily: if people open, reply and do not complain, your reputation rises; if they delete without reading or hit "report as spam", it drops fast.
Staying in the inbox
The good news is that these signals are largely within your control. Set up authentication for your domain, send from an address you have warmed up gradually, and write the way you would speak to a person, not like a brochure. A short, honest message sent to someone who has a reason to receive it triggers few complaints.
Target carefully too. Sending to off-topic contacts drives up deletions and reports, both poison for your reputation. Thirty relevant messages beat three hundred sent at random. Consistency helps as well: steady, measured sending reassures the filter far more than one big isolated blast.
How Kaptor helps you reach the inbox
Kaptor is aimed at local businesses and freelancers who have no time to become deliverability experts. The tool helps you target the right recipients by trade and area, which cuts down from the start the off-topic sends that trigger complaints. You send from your own mailbox, within a setup that favours plain, personalised messages.
To go further, learn what builds strong deliverability and why a well-crafted cold email clears the filters more easily.