Why do some emails go to spam?

Emails land in spam when mailbox providers (like Gmail, Outlook, or Yahoo Mail) decide your message looks risky or unwanted. They're not guessing. They're scoring hundreds of signals every time you hit send.

The signals fall into a few big categories:

Sender reputation. Your domain and sending IP have a history. If past emails from your setup triggered complaints, bounces, or low engagement, that reputation follows you. A poor reputation means the mailbox provider treats your new emails with suspicion (even if they're perfectly fine).

Engagement history. If people consistently ignore, delete, or mark your emails as spam, that tells mailbox providers your messages aren't wanted. Low open rates and high delete-without-reading rates hurt. Conversely, if people open your emails, reply, forward them, or move them to folders, that's a green flag.

Authentication setup. Broken or missing SPF, DKIM, or DMARC records make it easy for spammers to forge your domain. Mailbox providers penalize unauthenticated senders because they can't verify you're legitimate.

List quality. If your list includes spam traps, purchased contacts, or addresses that haven't engaged in years, you're sending to recipients who never wanted your emails. High bounce rates and complaint rates follow.

Sending patterns. Sudden volume spikes, inconsistent sending schedules, or switching domains without warming up the new one all trigger caution. Mailbox providers compare your current behavior to your history. Big changes look suspicious.

Content triggers. This one's overstated (engagement and reputation matter more), but yes, some content patterns raise flags. Emails that mimic phishing attempts (urgent subject lines, suspicious links, no real sender info) or look like bulk promotional mail with zero prior relationship get filtered. Content alone rarely causes spam placement for a sender with good reputation and engagement.

The most common mistake is thinking spam filtering is about one thing. It's not. You can have perfect authentication and still land in spam if your engagement is terrible. You can write beautiful emails and still get filtered if your domain reputation is shot. Spam filtering is a weighted combination of all these signals, and different mailbox providers weigh them differently.

So if your emails are going to spam right now, you need to figure out which signal (or signals) is the problem. Check your authentication setup first (it's the easiest to fix). Then look at your engagement metrics and list quality. You can check your SPF and DMARC with our free tools, or just ask us if you're stuck ;)