Is deliverability mostly about luck?

It doesn't feel like luck when everything's working. But the moment your open rates drop or a campaign vanishes into spam, it can start to feel pretty random. It's not. Deliverability is one of the most predictable systems in email, once you understand what inbox providers are actually measuring.

Inbox providers aren't mysterious. They're asking a simple question with every send: does this sender have permission to be here, and do the recipients actually want this? The signals they use to answer that question are almost entirely within your control.

Here's a quick diagnostic checklist. If your deliverability feels inconsistent, start here:

• Authentication. Have you published SPF, DKIM, and DMARC records for your sending domain? If any of these are missing or misconfigured, filters treat you as a stranger at the door. You can check your SPF in about 30 seconds with our free SPF checker.
• List quality. Are you sending to people who actually signed up, recently? Old lists, purchased contacts, or lists that haven't been cleaned in a year carry a lot of dead weight (and sometimes spam traps).
• Engagement rates. If a big chunk of your list hasn't opened anything in six months, those inactive addresses drag your reputation down with every send. Inbox providers notice.
• Complaint rates. A spam complaint rate above 0.1% starts causing real problems, especially at Gmail. Above 0.3% and you're in crisis territory.
• Sending patterns. Sudden spikes in volume, new IPs with no warmup, or wildly inconsistent cadence all look suspicious to filters.
• Content signals. Spammy subject lines, broken HTML, heavy image-to-text imbalance, and URLs that redirect through shady domains all add risk.

So what actually feels like luck? A few things genuinely can look random. Algorithm updates from inbox providers sometimes affect even healthy senders temporarily. Shared IP reputation at your ESP can shift if another sender on the same IP has a bad week. And filter quirks during a domain's early warmup period can feel unpredictable. But here's the thing: senders with strong fundamentals bounce back from these fast. Senders with weak fundamentals use these moments to explain away a longer-running problem.

The "luck" narrative is almost always a sign that one of the controllable factors above hasn't been looked at closely enough. (Of course, that's easier to say than to diagnose on your own.)

If you're staring at inconsistent results and not sure where to start, our SOS hotline is free. No pitch, just help figuring out what's actually going on.