Your custom tracking domain is the hidden reason your cold email deliverability tanked and how to diagnose it in 20 minutes
dns_regrets_oliver · 2026-09-21 · 0 views
I spent six weeks diagnosing a deliverability problem on one of my client accounts. Reply rates dropped from 3.8% to under 1%. GlockApps was showing 40% spam placement. Everything looked fine on the surface. SPF passing. DKIM passing. DMARC aligned.
The culprit was the custom tracking domain.
Here is what happened. The client had set up a custom click tracking domain months earlier on a different provider. That domain had been blacklisted due to abuse by other users on the shared tracking infrastructure. Every email that contained a tracked link was getting flagged before it hit the inbox.
How to check if your tracking domain is the problem. Run a GlockApps test with tracking enabled. Then run a second test with tracking completely disabled. If the second test shows dramatically better inbox placement, your tracking domain is the culprit. This diagnostic takes about 20 minutes and should be step one in any deliverability investigation where DNS checks out clean.
The fix options. First: disable all tracking entirely. No click tracking, no open tracking. The email arrives as plain text with no external pings. This will almost always improve deliverability immediately. Second: set up a clean custom tracking subdomain on a domain you own and control, something like track.yoursenddomain.com. This keeps the tracking domain reputation entirely in your hands going forward.
The honest advice. Stop tracking opens entirely. Apple MPP and security bots have made open rate data meaningless. Disable it and use reply rate as your only signal. Then seriously evaluate whether you even need click tracking. Most cold email practitioners who prioritize deliverability have removed it completely.
Your tracking domain is a piece of your deliverability stack that most people never look at. Check it before you blame your copy, your list, or your sending volume.