What causes a bad sender reputation?

Your sender reputation tanks when mailbox providers see patterns that scream "unwanted mail." It's not one mistake that kills you. It's a pattern. A few spam complaints might be noise, but if 0.5% of every send hits the spam button, that's a pattern. Bounces happen, but if 5% of your list doesn't exist, that's a pattern. Opens matter, but if 80% of your list hasn't opened in six months and you keep mailing them anyway, that's a pattern.

Here's what actually damages reputation, with the mechanisms behind each:

Spam complaints. Every "Report spam" click tells Gmail, Outlook, and Yahoo that recipients don't want your mail. Keep it under 0.1% or expect trouble. Above 0.3% and you're getting filtered or blocked outright.

High bounce rates. Sending to invalid addresses tells mailbox providers you don't maintain your list. Hard bounces (address doesn't exist) are the worst signal. If you're bouncing above 2%, you're flagging yourself as careless or malicious. Both hurt.

Low engagement over time. If recipients consistently ignore your mail (no opens, no clicks, straight to trash), mailbox providers assume it's not wanted. They'll start filtering it to spam or the Promotions tab. Mailing unengaged subscribers for months is one of the fastest reputation killers.

Sending to old or purchased lists. Purchased lists are full of people who never asked for your mail, which means spam complaints and spam trap hits. Old lists (untouched for 6+ months) decay fast. Addresses get abandoned, turned into spam traps, or just stop engaging. Either way, you're mailing people who don't want it.

Spam traps. These are email addresses that exist only to catch bad senders. No real person uses them. If you're hitting spam traps, it means you're either scraping addresses, buying lists, or never cleaning out old contacts. Mailbox providers and blocklists like Spamhaus watch for this closely.

Broken authentication. If your SPF, DKIM, or DMARC records don't align or pass, mailbox providers can't verify you're the real sender. That makes you look like a spammer or phisher. Failed authentication doesn't always block you immediately, but it absolutely hurts your reputation over time.

Sudden volume spikes. If you normally send 10,000 emails a week and suddenly jump to 100,000, mailbox providers see that as suspicious. They assume you bought a list, got hacked, or switched tactics. Volume changes need to be gradual (we call this warming), or your reputation takes a hit before mailbox providers figure out if the spike is legitimate.

Inconsistent sending patterns. Sending sporadically (nothing for weeks, then a blast, then silence again) makes mailbox providers distrust you. They can't build a reliable profile of your sending behavior, so they're more cautious with your mail. Regular cadence (even if it's just once a month) builds trust.

The fix starts with understanding your current state. Check your reputation, audit your authentication setup, and look at your engagement metrics (opens, clicks, complaints, bounces). If you're hitting any of the patterns above, stop mailing unengaged contacts, clean your list, and talk to us if you're stuck fixing authentication or unsure where to start.