There's a certain irony in building a service to help businesses get clients, only to find yourself fighting the very infrastructure that's supposed to deliver your message. i've spent months testing, tweaking, and pulling my hair out over email deliverability, and I've hit a wall that i can't scale. I'm hoping a second set of eyes can spot what I'm missing.

The setup

Running cold email for a B2B agency targeting other agencies, SaaS, and automation shops. mostly Google Workspace inboxes on the receiving end. two full batches of domains burned in exactly the same way. same infrastructure: Smartlead, Google Workspace mailboxes, domains from InboxKit, five mailboxes per domain. domain names are de-clustered, no obvious cousin variants, all redirect to my real company site with a Calendly link while i build out a proper VSL and proof of work.

copy is plain text, name-only signature, no links or images in the first email. Spintax and AI icebreakers, tracking off, randomized sends with three-minute gaps. Warmup: first batch got two weeks of Smartlead warmup, second batch got four weeks. Warmup stayed on, ramped from five to ten sends per day in weekly increments. lists are Sales Nav leads, verified with AnyMailFinder and Bouncer, Google inboxes only. Bounce rate sits between 0.4 and 1.5 percent.

What happens

Both batches follow the same script. Within the first week, domains get listed on SURBL under ABUSE. One domain per batch stays clean, always just one. everything looks great for about two weeks: 15 percent reply rate, 60 percent positive responses, warmup health reading 90 to 100 percent. then warmup health collapses almost overnight to 80 percent and keeps dropping. inbox placement tests to fresh seeds show SURBL-listed domains hitting zero out of ten inbox, ten out of ten spam. Dead.

What I've ruled out

SPF, DKIM, and DMARC all pass. Mail-tester scores 9 or 10 out of 10. The SURBL listing maps perfectly to the dead domains, while the one unlisted domain in each batch survives. the redirect target, my own domain, is clean on SURBL, so they're not inheriting the listing. Bounce rates are low, so the lists aren't full of dead addresses. same copy and same lists went to the survivor too. warmup health is a worthless signal below 98 percent, one domain read 96 percent while landing in spam on real seeds. even tried four-week warmed mailboxes instead of two, same story.

The part that doesn't add up

My aged brand domain, sent the exact same lists at the same volume, never burned. it lands in inbox on Workspace but spam on consumer Gmail. The fresh survivor does the same: inbox on Workspace, spam on normal Gmail. that's fine since all my lists are Workspace, but it's still a strange split.

My theories

Either pristine spam traps are hiding in the verified lists, and whichever domain's slice hits one gets SURBL-listed and dies first, or age and legitimacy are the real survival factors, and fresh domains can't earn Workspace trust through warmup alone. I've read that SURBL listing is a symptom, not the root cause, so what's actually causing the burn? why does one domain always survive while the rest die? And if its spam traps, how do you avoid them without going broke on verification costs? i've got a theory that the redirect to Calendly might be part of it, but I'm not sure. Appreciate any insights from folks who've navigated this.