Nick had a 35% open rate and a working system. He scaled volume from 75 to 225 emails per day on a single G Suite inbox. Combined with a 3-step sequence, total daily sends hit 675 from one address. Within weeks, emails stopped reaching inboxes entirely.
Nick ran B2B cold email sequences through HubSpot using a single G Suite inbox. The system was working — 35% open rate, consistent replies. He made one change: scaled sends from 75 to 225 per day to hit a 300/day target. With a 3-step sequence, that put 675 total emails per day on a single inbox. Gmail's safe cold sending threshold per mailbox is 50 to 80. Nick was running at 8x that limit. Reputation deteriorated over 2 to 3 weeks before the failure became visible. By the time he reached out, opens had collapsed and spam folder placement was near-total.
Single G Suite inbox carrying 675 cold sends per day — 8x over safe threshold. Sender reputation deteriorated progressively over several weeks before becoming visible in open rate data. SPF, DKIM, and DMARC were correctly configured, which is why the issue was not immediately obvious. The failure was pure volume architecture, not authentication.
Rebuild the sending infrastructure around the volume target rather than trying to fix the existing single-inbox setup. 3 dedicated sending domains, 6 mailboxes at 50 sends per day each = 300 daily sends distributed safely. All domains authenticated from scratch. Warmup ramp completed across all 6 inboxes before reconnecting to HubSpot sequences.
Confirmed the root cause was volume architecture, not DNS or copy. Sequences were performing fine. The inbox setup was not.
3 dedicated sending domains acquired. A records, MX records, SPF, DKIM, and DMARC configured on all three. Cloudflare DNS used for fast propagation.
6 Google Workspace mailboxes created across the 3 domains. Daily send limits set to 50 per mailbox. Rotation logic configured.
All 6 mailboxes enrolled in warmup via Mailreach. Ramp monitored daily across a 3-week schedule before any cold volume was added.
GlockApps inbox placement test run across Gmail, Outlook, and Yahoo. All 6 inboxes confirmed primary inbox landing before sequences were reactivated.
Sequences reconnected in HubSpot through the new authenticated inboxes. Volume reintroduced gradually at 50 per day per mailbox up to 300 total daily sends.
Open rate restored to 35% within 14 days of the infrastructure rebuild. 300 daily sends achieved safely across 6 mailboxes. Zero blacklist entries after rebuild. The system now has headroom to scale further by adding more domains and mailboxes without touching reputation.
Infrastructure rebuild completed in 14 days. Sequences reactivated with confirmed inbox placement across all major providers.30 minutes. No pitch. Walk away with a specific diagnosis and fix plan for your setup.