Every quarter, GlockApps publishes inbox placement numbers for the major consumer providers, and every quarter someone writes the aggregate headline. Q4 2025's aggregate story reads like good news: average inbox rates across AOL, Exchange/Office365, Gmail, Google Workspace, Hotmail, Outlook, and Yahoo rose 3-7% quarter over quarter. Cold email deliverability by sending volume tells a different story once you split that average by how much a sender actually mails. Senders sending 1,000 to 10,000 emails a month — the exact range most B2B outbound teams operate in, by design — lost Gmail ground even as the market average climbed. Senders mailing at real scale gained everywhere, and gained the most at Gmail and the Microsoft properties.
The Deliverability Split by Sending Volume
The topline number from GlockApps' Q4 2025 Email Deliverability Statistics report is that average inbox rates across major providers rose 3-7% quarter over quarter. Read at face value, that's a green light: deliverability is getting easier, providers are trusting senders more, whatever tightening happened earlier in 2025 is loosening. Most outbound teams will read that headline, feel reassured, and change nothing about how they send.
That reading misses the part of the report that actually matters for a B2B cold-email sender: the breakdown by sending volume tier. GlockApps segments results by how many emails a sender pushes per month — 1,000-10,000, 10,000-50,000, 200,000-1,000,000, and 1,000,000+ — and compares each tier's Q3-to-Q4 change. Those tier-level changes don't move together. The smallest tier, where the overwhelming majority of cold-outbound senders sit, moved in the opposite direction from the larger tiers at the two providers that matter most for B2B: Gmail and the Microsoft stack (Hotmail and Outlook).
This matters because most cold-email infrastructure advice — including advice we've given — is built around staying small. Spread volume across many domains. Cap sends per mailbox at 30-50 a day. Warm slowly. Look like a person, not a mail platform. That advice isn't wrong on its own terms; authentication and warmup hygiene still matter (see our cold email deliverability playbook for the mechanics). But the Q4 2025 tier data raises a real question about whether the low-and-slow, maximally-fragmented sending pattern is still the safest posture at Gmail and Microsoft, or whether it's now the pattern getting the least benefit of the doubt.
Where Inbox Placement Landed in Q4 2025
Before getting into the tier breakdown, it's worth anchoring on where inbox placement actually landed across providers in Q4 2025, in absolute terms — not the change, the level. These are GlockApps' overall average inbox placement rates for the quarter, blended across all sender volumes:
Two things stand out. First, none of the four providers cracked 60% average inbox placement — meaning that, blended across every sender in GlockApps' panel, roughly four in ten to five in ten test emails landed somewhere other than the primary inbox. Second, the Microsoft properties trail Gmail and Yahoo by a wide margin: Outlook's 45.06% and Hotmail's 46.79% sit more than ten points below Yahoo's 57.48%. If your prospect list skews toward Microsoft-hosted business domains, which most enterprise and mid-market B2B lists do, your baseline placement problem is worse than the Gmail-focused conversation in most cold-email advice assumes.
These are levels, not trends — they tell you where you're starting, not where you're headed. The tier data below is what tells you where you're headed, and it's the part that actually changes what a sending strategy should look like going into the next quarter.
The Small-Sender Penalty at Gmail and Microsoft
Here's the tier breakdown that the aggregate 3-7% headline is hiding. GlockApps reports Q3-to-Q4 2025 change by sending volume tier, and the smallest tier — 1,000 to 10,000 emails a month, which covers nearly every cold-outbound program running from a handful of mailboxes — moved backward at exactly the providers B2B senders care about most.
| SENDING VOLUME TIER | GMAIL / GOOGLE WORKSPACE | MICROSOFT (HOTMAIL / OUTLOOK) | YAHOO / AOL |
|---|---|---|---|
| 1,000–10,000 / month | Gmail −15%, Google Workspace −19% | Not broken out separately at this tier | AOL +24%, Yahoo +26% |
| 10,000–50,000 / month | Gmail +17% | Hotmail −14%, Outlook −14% | Yahoo −14%, AOL −13% |
| 200,000–1,000,000 / month | Gains across the board (Office365 +14%) | Hotmail +15%, Outlook +15% | Gains across the board |
| 1,000,000+ / month | Gmail +20% (largest gain of any tier/provider pair) | Gains across the board | Gains across the board |
At the 1,000-10,000/month tier — the classic cold-outbound range, chosen specifically because it's supposed to read as small and human rather than as bulk mail — Gmail inbox placement dropped 15% quarter over quarter and Google Workspace dropped 19%. Meanwhile AOL and Yahoo inbox placement at that same small-sender tier rose 24% and 26% respectively. So the smallest senders didn't get penalized everywhere; they got penalized specifically at Gmail and Google Workspace, which is where the majority of B2B decision-makers and technical buyers actually read their mail, whether through a personal Gmail account or a Google Workspace-hosted company domain.
Why High-Volume Senders Are Winning the Inbox
The tiers above 10,000 emails a month tell a more consistent story, and it runs opposite to the small-sender tier. At 10,000-50,000 a month, Gmail inbox placement actually rose 17% — a reversal from the smallest tier's decline — while Hotmail, Outlook, and Yahoo all dropped 14% and AOL dropped 13%. That's a mixed quarter for this middle tier, but it's already a different pattern than the bottom tier: Gmail rewarding more volume, not less.
Above that, the pattern stops being mixed and becomes uniform. At 200,000-1,000,000 emails a month, inbox placement increased for every major provider GlockApps tracked, with the biggest gains at Hotmail and Outlook (+15% each) and Office365 (+14%). At 1,000,000+ emails a month, placement again increased across every provider, and the single largest gain in the entire report — +20% — went to Gmail at this top tier. Put the two ends of the range next to each other: the smallest senders lost 15-19% at Gmail while the largest senders gained 20% at Gmail, in the same quarter.
That's the opposite of what most cold-email operators assume is happening. The working theory in most outbound playbooks is that inbox providers are hunting for bulk-sender signatures and punishing anything that looks like scale, which is why the standard defense is to look small — low daily volume per mailbox, many separate sending domains, slow warmup, minimal similarity between messages. The Q4 2025 tier data suggests Gmail and the Microsoft properties are doing something closer to the reverse at the extremes: rewarding senders whose volume is large enough, and presumably consistent enough, to read as an established and monitored sending operation, while giving less benefit of the doubt to senders whose volume is small enough to be indistinguishable from a first-time or disposable sender.
None of this is proof of a documented policy shift — GlockApps' report doesn't state why the tiers moved apart, and providers don't publish the internals of their reputation models. But a director-level pattern this consistent, across two full quarters of comparison and the two provider clusters that carry the most B2B mail, is worth treating as a real signal rather than noise.
What Sending Volume Means for Your Infrastructure
If your outbound program is built the standard way — several mailboxes, low volume per mailbox, spread across a handful of purchased domains — this data is a reason to test consolidation, not to panic and rebuild everything. The practical moves:
This isn't an argument for buying a dozen new domains and blasting volume through them. It's an argument for testing whether the volume you're already sending would perform better concentrated through fewer, properly authenticated, actively monitored sending identities than spread thin across many. If you're not sure where your program currently sits on the volume-versus-fragmentation spectrum, an outside pass on your current setup — the kind we run through our cold email deliverability service — will tell you which tier you're actually in per domain, not just in aggregate, and where the biggest placement gap is by provider.
Reporting matters here as much as the sending change itself. A program that can't see inbox placement broken out by provider and by domain won't catch a Gmail-specific decline until reply rates have already dropped — by which point you've lost weeks of pipeline data on a change you could have caught in days. That's the same argument we make for reporting and analytics generally: the metric that matters is the one broken down finely enough to act on, not the one that looks fine blended together.
A Directional Read, Not a Permanent Verdict
One quarter of tier data is a signal worth testing, not a rule to build a permanent architecture around. GlockApps' Q3-to-Q4 comparison could partly reflect seasonal list quality, a handful of large senders skewing the top tiers, or a temporary tightening at Gmail that eases again next quarter. The honest caveat stands: these are percentage changes in placement rate, not absolute placement levels, and a tier that gained 20% from a low base isn't necessarily beating a tier that held flat from a high one.
What doesn't require more data to act on is the mismatch between the conventional cold-email playbook and what actually happened at Gmail and Microsoft in Q4 2025. If your program is built entirely around the assumption that smaller and more fragmented is always safer, that assumption just took a real hit at the two provider clusters that carry most B2B mail. It's worth testing the opposite for a quarter — consolidated, well-authenticated, properly warmed volume through fewer domains — and measuring inbox placement by provider before and after, the same way GlockApps measured it.
“The senders who gained the most in Q4 2025 weren't the smallest or the most fragmented. They were the ones sending enough, consistently enough, to look monitored.”
Do this next: pull your current sending volume per domain and per mailbox for the past 30 days, sort it against the four tiers above, and check where you actually sit — most teams assume they're smaller or larger than they are. If you're squarely in the 1,000-10,000/month tier with several thin domains, run a four-week test consolidating a portion of that volume onto two or three well-authenticated, actively warmed domains, and track Gmail and Microsoft inbox placement separately, not blended. If your outbound program leans B2B SaaS or technology accounts, where Microsoft-hosted business domains are common on the prospect side, weight that comparison toward Outlook and Hotmail placement specifically — that's where the absolute placement gap is widest and the tier-level upside is largest.
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