2026-09-23 · IPV4 Scanner
You send a perfectly normal email and it lands in spam. Nobody reported it, nothing about it was shady, and the filter still ruled against you. Spam filtering is a scoring system with a lot of inputs, and a legitimate message can lose on the total while being innocent on every single line.
Here's what actually moves the score, roughly in the order I'd check it.
This is the first thing a receiver looks at and the most common thing you can actually fix. If your domain has no SPF, DKIM or DMARC, you look exactly like a spoofer, because spoofers are the reason those records were invented in the first place.
The sneaky version is worse than the missing one. An SPF record that's drifted past its ten-lookup limit, a DKIM signature that no longer matches, a DMARC policy pointing at the wrong domain: all of these fail silently. Everything looks configured. It just doesn't pass. Check all three before you go hunting for anything more exotic.
Providers keep a running score for every sending IP and domain, built from how people reacted to your past mail. Land in enough spam folders, collect enough "mark as spam" clicks, and the score drops until you're filtered before anyone even sees the message.
Reputation is why a brand-new domain or a fresh server IP tends to struggle at first. No history reads as mild suspicion. It's also why a shared IP on budget hosting can sink you through no fault of your own, since you inherit whatever the other people sending from that IP have been up to.
DNS blacklists are lists of IPs known for spam, and mail servers check them on every connection. You can land on one from a genuinely infected machine on your network, from a shared IP a neighbour abused, or just from sending on a residential connection that's listed by policy.
Our IP blacklist checker tells you whether your sending IP is listed. Weigh the answer by which list flagged you. A big, widely-used list genuinely hurts delivery. An obscure one almost nobody queries might be doing nothing at all.
Content matters less than the folklore says, but it isn't nothing. The real triggers aren't "spammy words," since filters moved past keyword lists a long time ago. They're structural. A single big image with almost no text, which is how a lot of spam hides its message from anything that reads text. Link shorteners, or links where the visible text points somewhere different from the actual URL. Broken HTML with no plain-text version. A subject line that has nothing to do with the body.
Providers watch what recipients do. Mail that gets opened and replied to builds you up. Mail that gets deleted unread, ignored, or marked as spam tears you down. Sending to old or bought or dead lists is one of the fastest ways to train the filters against yourself, because low engagement looks identical to unwanted mail from the outside.
Start with authentication, because it's the highest-impact step and it's entirely yours to control. Then check for blacklisting, and if you're listed, find and fix the cause before asking to be removed. Ask while the problem's still there and you'll just get relisted, sometimes for longer. After that, send through a reputable service instead of a raw server or a home connection, so you inherit a maintained reputation rather than building one from zero. Clean the dead addresses off your list. And if you're on a new domain or IP, warm it up slowly rather than blasting your whole list on day one.
Why does one provider deliver my mail and another spams it?
Each one scores independently, with its own weights and its own view of your reputation. Passing Gmail tells you nothing about Outlook, which is stricter on some signals and looser on others.
I only send a handful of personal emails. Why do they get filtered?
Usually authentication or the IP you're sending from. A personal domain with no SPF or DKIM, or mail sent from a home connection that's on a blacklist by policy, will struggle no matter how little you send. Going through a real mail provider fixes most of it.
Do spam trigger words still matter?
Much less than the myth. Filters weigh authentication, reputation and engagement far above vocabulary now. An image-only email hurts you more than any single word ever will.
How long does it take to recover a bad reputation?
Weeks of steady, wanted mail, not days. Reputation builds slowly and drops fast, and there's no reset button. All you can do is send mail people actually want, consistently, until the score climbs back.
Does a blacklist listing hurt my website too?
Almost never. DNS blacklists are a mail-server thing, so a listing hits your email, not ordinary web traffic to your site.