How inbox providers treat different emails

“Marketo and some other ESPs send all your emails to spam.” Don't they? Your ESP does impact deliverability; but not in the way most marketers think. Inbox providers don’t hate Marketo. They distrust bad senders. Marketo, HubSpot, Mailchimp, Klaviyo, all host thousands of senders. If you’re on a shared IP with shady neighbors, inbox providers might punish you too. Let’s be honest: some ESPs are just plain bad. 1. They let anyone send, no vetting, no compliance, no limits. 2. Their IP ranges show up repeatedly on blocklists. 3. Their support shrugs off your inboxing issues with generic answers. Red flag: If your ESP doesn't care who sends what, you’re sharing reputation with spammers. Dedicated IPs help, but they’re not magic. A dedicated IP in a “bad neighborhood” still inherits risk. Without proper warmup, domain alignment, and consistent volume, you're still a stranger to mailbox providers. Think of it like buying a premium car but driving through a toxic zone, you're not protected. The real issue isn’t always the platform, it’s the sending. Switching ESPs won’t fix your deliverability if your: 1. Domain reputation is weak 2. Lists are stale or purchased 3. Content is clickbait 4. Engagement is low These follow you wherever you go. That said, some ESPs are stuck in the past. If your platform doesn’t offer: 1. Custom Return-Path 2. ARC header support 3. Reliable bounce categorization 4. Fast IP warm-up tools 5. Responsive deliverability support Then yes, that’s a reason to leave. So what does drive inbox placement? Focus on these fundamentals: 1. Domain-level reputation and alignment (SPF, DKIM, DMARC) 2. Strong engagement signals (opens, clicks, replies) 3. Clean, opt-in-only lists 4. Consistent volume and sending patterns 5. Fast bounce/suppression handling 6. Relevant, non-spammy content Blaming your ESP is easy. But sometimes, they do deserve it. If your setup is right, but inboxing still fails, ask: 1. Who else is sending from this subnet? 2. Is the ESP proactive with abuse management? 3. Are they helping or just blaming Gmail? If your ESP doesn’t protect your reputation, you need to protect yourself, by leaving. Bottom line: The ESP is your infrastructure. Your deliverability is your responsibility, but if the infrastructure is broken, no amount of sender best practices can fix it. Have you dealt with shady ESPs or deliverability disasters? Let’s talk. #emailmarketing #deliverability #ESP #marketo #inboxstrategy #emailtruths #email

There's an ongoing debate about whether marketers should aim for Gmail's Primary tab versus Promotions. Same at Apple (Primary vs Promotions), Outlook (Focused vs Other), and Yahoo (Primary vs Offers). Our guidance at Validity Inc. has always been clear: Subscribers generally expect marketing emails in Promotions, and attempts to game the system get punished by mailbox providers. (Gmail, Microsoft & Yahoo were unequivocal about this during our "Inbox Decoded" session at Litmus Live!) Recently we got real-life insight when a Gmail issue saw all promotional emails delivered to Primary for two days. Cordial's Steven Lunniss analysed what happened: a mild uplift in open rates, but unsubscribes spiked more than 50% above the baseline. He makes an excellent point: "When a subscriber opens your email in the Promotions tab, it is because they're ready to browse offers. That is infinitely more valuable than someone who opens it in Primary because it interrupts their workflow. The former is a warm lead, the latter is a person with their finger hovering over Unsubscribe." This shows exactly why trying to manipulate tab placement backfires. Subscribers have organised their inboxes intentionally. When you're in Promotions, you're reaching people in buying mode. Force your way into Primary, and you're interrupting people who aren't. Better engagement in the right tab beats forced visibility in the wrong one. What's your take on the Primary versus Promotions debate?

Is your mail sliding into the spam folder? Has your reputation slipped to "low" in Google Postmaster Tools? Does Microsoft SNDS think you stink like a kid who just came in from recess? Well, I have good news and bad news. 🟢 Good first: Most major mailbox providers (MBPs) provide methods of contacting them! Gmail, Microsoft, Yahoo, Comcast, Apple (and more!) all offer sender support forms or publish postmaster email addresses so that you can reach out directly when you're encountering an issue delivering mail to their users. 🔴 Now for the bad: These MBPs receive a ton of submissions, most of them from spammers. They already have information on your traffic, which is why you're blocked or bulked in the first place. They're not going to just fix whatever problem you're having because you asked nicely. They're definitely not going to fix it if you're being rude. They don't care about your business model, or your bottom line, or your legal requirements. What they care most about is their own customers. And if you're sending to the right people, then those people are also *your* customers, and you should care about them, too! So, even though it's an option to ask the MBP for help, it's probably not the first (or best) one, because all the evidence they have available so far indicates that your mail is potentially dangerous, and maybe you are too. Your job now is to demonstrate that they got it wrong, ideally using your actions and not just words. Before submitting that sender contact form, review the MBP's guidelines and your own practices. After all, their playground, their rules! Each MBP has its own quirks, but the basics tend to be the same. If you're not sure where to start, it's here! 🛝 Rule 1: Keep spam complaints as low as possible. The best way to do that? Get permission, always. Maintain a healthy list by removing bounces and sending to your most-engaged subscribers. Make it easy to unsubscribe, and honor unsubscribe requests when you get them. 🛝 Rule 2: Authenticate your mail. Use SPF, DKIM, and DMARC so you earn the deliverability you deserve (and don't forget to actually review your DMARC reports!). Authentication doesn't guarantee inbox placement, but you'll be left in the dust without it. 🛝 Rule 3: Be predictably yourself. MBPs and subscribers both reward consistency, and results tend to be stronger when everyone knows what to expect, when. Send similar volumes at similar times on similar days, ensuring increases are gradual to give the filters (and the audience) time to adjust. If you're ramping up and see increased delays, blocks, or complaints, or lower opens than expected, slow down and reassess. It's possible that the segment is no longer viable, or requires a different approach. If these bases are covered, THEN you can reach out. Include your name, your company, your domain & IP, the specific outcome you're having (including the bounce reason, if applicable), and what you've done to improve. And be nice!

Same domain. Same content. One inbox. One spam folder. Here's what we discovered testing our sales team's emails last week. 👇🏻 We had two reps. Both were using the company domain.  Both were sending identical cold emails. Rep A: Spam folder every time. Rep B: Inbox consistently. We checked everything: • Blacklists? None. • Domain reputation? Clean. • SPF, DKIM, DMARC? All passing. Then we dug into Microsoft's header data. The reality is that Microsoft doesn't just score your domain. They score your individual mailbox. Rep A had built a bad reputation over time without realizing it: • Three phone numbers in his signature (all different area codes) • History of sending PDF attachments • The word "hotline" in his contact info • Multiple typos across past emails His mailbox got flagged. Not the domain. His specific email address. Microsoft assigned his mailbox a higher spam confidence score. Same domain as his colleague, completely different treatment. What this means for you: If you're doing inbox placement tests, don't just test your domain. Test each sender's actual mailbox. Your domain might be clean, but your individual sending history matters just as much. Three ways to protect your mailbox reputation: 1️⃣ Keep your signature clean and simple. No random phone numbers or suspicious terms. 2️⃣ Don't send large attachments from your cold outreach mailbox. Ever. 3️⃣ Use a separate domain for prospecting. Your main company domain shouldn't touch cold email. And if you're not running consistent warm-up with real engagement? Your mailbox reputation will tank faster than you think. Microsoft is tracking you at the mailbox level. Act accordingly. Have you noticed different results from different senders on the same domain? 

What you need to know about Google’s AI-powered inboxes   Is cold email dead? That’s the current panic, but it’s not the right way to look at this.   Google didn’t remove email or block outbound.   What changed is how attention is allocated inside the inbox.   Instead of a purely chronological list, Gmail is introducing a prioritization layer that helps surface what looks important and actionable.   That prioritization is informed by signals such as:   → existing threads and reply history → people the user interacts with most → messages that appear time-sensitive or task-driven → updates that look informational rather than action-oriented   All emails still arrive. But not all emails are treated the same once they do.   For outbound and GTM teams, this shifts what actually gets seen.   Inboxes become more sensitive to intent and context.   Emails tied to real signals and a clear reason for outreach are more likely to surface.   Low-context, volume-driven emails don’t necessarily go to spam, but they lose attention.   So this is less about email becoming harder, and more about inboxes becoming more selective.   ❌ Messages without context fade into the background. ✅ Messages that arrive for a reason, at the right moment, stand out.   In that sense, Google’s AI-powered inboxes don’t punish outbound. They reward relevance.   And for teams already building signal-first GTM motions, this is likely a net positive!

Someone introduced me to a woman whose emails kept landing in spam. She wasn't doing anything obviously wrong. She was sending from Google Workspace. Professional setup, or so she thought. I checked her records. Two things were missing - and once I saw them, the problem made complete sense. Here's the way I like to explain email authentication: Think of every email you send as a traveler arriving at passport control. The inbox provider - Gmail, Outlook, Yahoo -is the officer at the desk. Their job is to decide - is this traveler legitimate? Are their documents valid? And what do we do if something looks wrong? SPF is the list of who's actually allowed to travel on your passport. It tells inbox providers which programs - your email platform, your website, your booking tool - are authorized to send on behalf of your domain. If a sender isn't on the list, that's a red flag. DKIM is the official seal on the document. It proves the email actually came from you, and that nobody tampered with it in transit. DMARC is the passport control policy. It tells inbox providers what to do if something doesn't pass inspection - let it through, send it to spam, or reject it entirely. It also creates a reporting system, so you can see when something goes wrong and investigate. This woman was missing her DKIM and DMARC. So inbox providers had no seal to verify, and no instructions to follow. They made their own call. Spam folder. The fix wasn't complicated. But she had no idea it was broken. This isn't just an email marketing problem, by the way. It affects every email you send from your domain - including your regular work emails from Google Workspace. If you're not sure whether your own setup is solid, DM me the word CHECK and I'll point you in the right direction.

"Our email is performing great." That's what a founder told me last month. His Gmail open rates were 55%+. His Hotmail opens were in the low 20s. He had no idea. Overall open rate was 45%. Revenue was growing. Everything looked fine on the surface. Then I pulled the data by inbox provider. Gmail was carrying the entire channel. Hotmail and Outlook were in the low 20s. Thousands of emails going out every week that basically didn't exist since they’re hitting spam. I see this all the time when I audit accounts. Brands crushing it in Gmail and completely invisible in other inboxes. Their overall numbers look fine, so they never dig deeper. Your segmentation, your creative, your offers. All of it is invisible if it's landing in spam. Here's how you actually fix it: → Split your reporting by inbox provider. Stop looking at overall metrics. See who's opening where. You can't fix what you can't see. → Tighten the engagement window for problem domains. If Hotmail's underperforming, don't send to your full 90-day engaged segment there. Tighten it to 14-30 days. Send less, but send to people who are actually opening. Build the reputation back slowly. → Mix in plain-text emails. Especially at the end of abandonment flows. They feel more personal, they're lighter on code, and inbox providers trust them more. I've seen plain-text outperform designed emails in almost every sunset and win-back sequence I've built. Deliverability isn't the exciting part of email. But it's the backbone of everything else working. This is very important to nail alongside improving everything else. 

After nearly 2 decades in the world of email, there's one question I still get asked more than any other: “What actually impacts deliverability?” It's the email world's equivalent of "what's the meaning of life?". Everyone's got an opinion, but very few can explain it without looking like Charlie from It's Always Sunny. Here's the short version of what I've learned: Engagement is the real boss fight. Inbox providers are watching how people interact. That's opens, clicks, replies, and even dragging you out of spam. That’s what tells them your emails deserve a seat at the inbox table. Relevance can beat personalization. You don’t need someone's name in three places. You need to send content they actually care about. Relevance drives engagement, and engagement drives deliverability. Your tech setup? It's the entry fee, not the trophy. SPF, DKIM, and DMARC matter. But they can't save weak content or erratic sending patterns. And yes, recovery is possible. If you burn a domain or subdomain, you can rebuild. Slowly. Thoughtfully. Inbox trust comes back through consistency and accountability, not volume. The truth is, there's no secret formula. Inbox providers reward patience, relevance, and accountability. Which just so happen to be the same traits that define good lifecycle marketing. I recently unpacked all this (and more) with the Lifecycle Leaders crew. Everything from domain warm-up, recovery, engagement, and beyond. You can read the full breakdown when you subscribe: https://lnkd.in/gQ6x8Qja

Before copy, before offers, before personalization… your emails need to land in the inbox If you're doing [X] - sending emails straight from a fresh domain without setup Switch to warming and proper infrastructure first, because inbox providers will flag you immediately. 1. Disable Tracking Links Tracking pixels and link tracking often trigger spam filters. They add extra redirects → suspicious behavior They signal “mass outreach tool” What works: Use plain links or no links at all in the first email. Focus on getting a reply, not a click. 2. Use Multiple Mailboxes per Domain One inbox blasting emails = high risk. Spread volume across 2–3 inboxes per domain Example: john@ mike@ Why it matters: Lower activity per inbox = more natural sending pattern. 3. Mix Google and Outlook Accounts Email providers watch patterns. If all your emails come from one ecosystem, it’s easier to detect. Better approach: 50% Google Workspace 50% Outlook This creates diversity and reduces risk signals. 4. Warm Up Your Domains (Minimum 2 Weeks) New domains have zero trust. If you're doing [X] sending emails immediately after setup - switch to warming first, because cold domains get flagged fast. Simple process: Start with 5–10 emails/day Gradually increase Use real conversations or warm-up tools Goal: build history that looks human. 5. Use Separate Domains for Outreach Never send cold emails from your main domain. Why: Protect your brand domain reputation Avoid affecting your core business emails Example: Main: yourcompany.com Outreach: yourcompany.co / getyourcompany.com 6. Set Up SPF, DKIM, and DMARC Properly Skip this and your emails won’t be trusted. These are your authentication signals: SPF → confirms sender DKIM → verifies message integrity DMARC → tells servers how to handle failures No setup = low deliverability, even with great copy 7. Keep Volume Low (Max ~20 Emails/Day per Inbox) More volume doesn’t mean more results. Among outbound campaigns, accounts sending lower daily volume tend to last longer and perform better. What works: 10–20 emails per inbox per day Scale by adding inboxes, not volume That's it!

Two years ago, cold email was simple. Buy a list. Load it up. Hit send. Hope for replies. It worked. Not because the emails were good. Because the filters were weak. That's over. Google and Microsoft have completely changed how they decide what reaches the inbox. They're looking at sender reputation, engagement history, domain age, authentication, sending patterns — everything. And one by one, the old habits are dying: 𝗦𝗽𝗿𝗮𝘆 𝗮𝗻𝗱 𝗽𝗿𝗮𝘆 — sending 5,000 emails to a list you barely filtered. ESPs now punish low engagement. If most people ignore your emails, your next batch goes straight to spam. 𝗢𝗻𝗲 𝗱𝗼𝗺𝗮𝗶𝗻, 𝗼𝗻𝗲 𝗶𝗻𝗯𝗼𝘅 — running all your outreach from one account. One spam complaint and your entire outbound goes dark. 𝗡𝗼 𝘄𝗮𝗿𝗺-𝘂𝗽 — sending cold emails from a brand new account. ESPs see a stranger showing up with 200 messages on day one. That's not sales. That's spam. 𝗠𝗮𝗻𝘂𝗮𝗹 𝗳𝗼𝗹𝗹𝗼𝘄-𝘂𝗽𝘀 — following up when you remember instead of when the prospect is most likely to respond. Timing is half of deliverability. 𝗕𝘂𝘆𝗶𝗻𝗴 𝘂𝗻𝘃𝗲𝗿𝗶𝗳𝗶𝗲𝗱 𝗹𝗶𝘀𝘁𝘀 — every bounced email hurts your sender score. Enough bounces and ESPs stop trusting you entirely. The teams still doing outbound well in 2025 aren't writing better emails. They're treating infrastructure like a product. Not an afterthought. Which door are you still behind?