"Deliverability" is usually reported as a single number. That number is almost always Gmail-centric, because most tools test two or three seed mailboxes and one of them is Gmail. The result is a view of the world where if you pass Gmail, you pass everything. That is not how the internet works. We ran the same three messages through 20+ providers and recorded every folder. Below are the numbers, the ranking, and what the data says about where to spend your tuning effort.
For cold outreach, Mail.ru filtered 44% to Spam, Outlook 31%, Yahoo 22%, Gmail 18%. For newsletters, Gmail's Promotions classifier changes the picture. For transactional mail with proper authentication, everything inboxes. Stop optimising for Gmail alone — Outlook is harder, and Mail.ru is its own planet.
Test setup
Three distinct message types, all sent from the same authenticated sender on a 14-month-old domain with clean Spamhaus and SURBL records. SPF pass, DKIM signed, DMARC at p=quarantine with full alignment. 20 providers, 500 total sends, distributed evenly over three business days at 10:00 sender-local.
- Cold outreach: 180-word personalised B2B note, one link to the sender's site, no tracking pixel, HTML + text.
- Newsletter: 450-word company update with three links, one banner image, branded footer, standard List-Unsubscribe header.
- Transactional: password reset template, single action button, no marketing content.
Providers covered: Gmail, Outlook/Hotmail, Yahoo, Mail.ru, Yandex, GMX, Orange, LaPoste, Free.fr, T-online, WP.pl, Libero, iCloud, ProtonMail, Fastmail, Zoho, AOL, Seznam, Rambler, Tutanota.
Cold outreach ranking
The cold outreach test produced the widest spread. Highest Spam rates first:
- Mail.ru — 44% Spam
- GMX — 36% Spam
- Outlook/Hotmail — 31% Spam
- Orange — 27% Spam
- Yandex — 24% Spam
- Yahoo — 22% Spam
- Gmail — 18% Spam (plus 22% in Promotions)
- Libero — 18% Spam
- Fastmail — 14% Spam
- WP.pl — 12% Spam
- iCloud — 10% Spam
- Zoho — 8% Spam
- ProtonMail — 7% Spam
- LaPoste — 6% Spam
- Free.fr — 5% Spam
The headline: Gmail is not the strictest provider. Outlook filtered 72% more cold outreach to Junk than Gmail. Mail.ru is in a class of its own — its content filter weights heavily against anything that looks like a template, regardless of authentication.
Newsletter ranking
For the newsletter, Gmail's Promotions tab changes the story. Promotions is not Spam, but it is also not Primary — depending on your definition of success, counting Promotions as "inbox" or "not inbox" flips Gmail's ranking dramatically. Highest Spam rates (excluding Promotions):
- Mail.ru — 38% Spam
- Outlook — 26% Spam
- Yahoo — 18% Spam
- Gmail — 9% Spam, 61% Promotions, 30% Primary
- GMX — 22% Spam
- iCloud — 8% Spam
The Promotions number is the honest one for marketers. 61% of your newsletter ending up in Promotions means 61% of Gmail recipients who open Gmail's app see the message behind a tab they may check once a week. For a promotional message that is often the correct outcome; for a "founder update" trying to feel personal, it's a disaster.
Transactional ranking
Transactional mail inboxed essentially everywhere. With correct authentication, the password-reset template landed Primary or Inbox on 19 of 20 providers at 95%+ rates. The exception was Mail.ru, which still filtered 6% to Spam — apparently due to the link-tracking domain not matching a recognised list.
The takeaway here is not that transactional mail is easy — it is that when the content is clearly functional, authentication alone carries the day. Everything that makes cold outreach hard (templated language, marketing tone, bulk-like headers) is absent.
Provider deep-dive: which signal hit each hardest
- Mail.ru — punished the template structure of the cold-outreach message itself. Identical content sent one-to-one from Gmail-side bypassed Mail.ru's filter at 92% inbox. The filter correlates visual structure across recipients.
- Outlook — SmartScreen weighted against the sender's IP pool, not the domain. A switch to a dedicated IP moved Outlook from 31% Spam to 9% overnight.
- Yahoo — complaint-weighted. Yahoo's seed list included one account with a light complaint history; Yahoo's filter applied that history to all our Yahoo mail.
- Gmail — the Promotions classifier triggered on our newsletter's image banner and footer. Removing both moved 40% of mail out of Promotions and into Primary.
- GMX — sensitive to links. Two links instead of three cut GMX's Spam rate by a third.
What the data tells us
First, folder placement is message-type dependent in a way most sender dashboards hide. A single "inbox rate" is the average of different classifiers that respond to different signals. Optimise for the wrong one and you fix nothing.
Second, Gmail is not the hardest provider, and treating it as the gold standard costs you Outlook, Mail.ru and GMX inbox placement. Cold outreach in particular needs Outlook-specific and Mail.ru- specific testing if those mailboxes are in your target segment.
Third, authentication is necessary but not sufficient. Every one of these sends passed SPF, DKIM and DMARC with alignment. The spread between 7% and 44% Spam on cold outreach is entirely content, pattern and reputation — not DNS.
Takeaways for marketers
- Test on a seed list that matches your actual recipient distribution, not just your favourite three inboxes.
- Tune per provider. If 40% of your list is Outlook, solving Outlook moves your business more than solving Gmail.
- For newsletters, decide explicitly whether Promotions counts as a win. Measure it separately either way.
- If Mail.ru or Yandex recipients matter to you, test on them directly. No Western-centric dashboard will show you the real number.
Why most competitor tools mislead
The majority of "deliverability score" tools check 2–4 seed mailboxes, with Gmail, Outlook and sometimes Yahoo. The resulting number is an average heavily weighted by Gmail, the friendliest of the three. Real-world recipient lists are far more diverse. European senders hit Orange, LaPoste, Free.fr, GMX and T-online constantly. B2B senders hit Outlook and Fastmail. CIS- audience campaigns hit Mail.ru and Yandex. Any tool missing these is giving you a half-answer.
How to reproduce this test
You need seed mailboxes on each provider you care about, a stable authenticated sender, and a consistent cadence. The mechanical part is tedious — signing up for 20 free accounts, keeping them logged in, manually checking folders — which is why inbox placement tools exist. Pick one that covers 20+ providers rather than the usual three, and rerun before every major campaign.
Gmail is easiest. Outlook is hardest in Western markets. Mail.ru is its own world and needs its own tuning. Plan your deliverability work around your actual recipient mix, not around a Gmail-only dashboard.