Most cold email issues start long before a message hits spam. Gmail and Outlook score every sender the moment an email leaves the server, and they do it with far more nuance than most people think.
If anything you do resembles behavior they’ve seen from questionable senders, your deliverability drops. If your behavior looks normal and predictable, inboxing becomes a lot easier.
Fortunately, their filtering logic becomes predictable once you understand what they look for.
It’s easy to treat deliverability as a checklist. Set up SPF, DKIM, and DMARC, warm the domain for a couple of weeks, and call it a day.
These things matter, but they don’t determine inbox vs. spam on their own.
They simply give Gmail and Outlook enough information to evaluate you accurately.
The real deciding factor is behavior. Providers want to see a sender who looks human, consistent, and welcomed by recipients — not someone pushing aggressive volume through a new domain or blasting the same template everyone else uses.
Inbox providers begin with identity checks. SPF tells them which servers can send for you. DKIM verifies the message wasn’t altered. DMARC ties everything together.
Reverse DNS adds another signal of legitimacy.
This doesn’t guarantee inbox placement, but without these pieces, reputation builds slowly. It’s like arriving somewhere official without proper ID. You may get through eventually, but you’re getting extra scrutiny.
Mailivery has full walkthroughs if you need them: SPF, DKIM & DMARC Setup Guide for Email Deliverability, Why an SPF Record Is Important, and several provider-specific SPF tutorials.
After Gmail and Outlook confirm your identity, the real focus shifts to how you’ve behaved over time.
Every domain and IP builds reputation based on:
Reputation doesn’t reset quickly. A domain with poor history won’t recover in a day, and a well-warmed domain won’t collapse instantly either.
This is why warming up before cold outreach isn’t optional…it sets the baseline you build from.
Gmail and Outlook pay close attention to patterns. Real people don’t send with perfect timing, and they don’t scale from 10 emails to 600 overnight. They also don’t blast identical content across multiple tools at the same time.
If your activity looks mechanical, filters tighten. If it looks like natural communication, filters ease up.
Warmup helps here because it establishes a rhythm. Gradual increases, real conversations, and timing that doesn’t resemble automation all contribute to trust.
Outlook is more sensitive to sudden volume changes. Gmail is more sensitive to content and engagement shifts.
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Engagement carries more weight than most senders expect.
Opens matter a little, but Gmail and Outlook focus more on deliberate actions:
Those actions tell the system that recipients want your messages in the inbox. Low engagement, especially deletes without reading, tells the opposite story.
This is a big reason cold email hurts so many domains. When reply rates are consistently low, filters lose confidence in the sender.
For more guidance: 5 Reasons Your Cold Email Reply Rate Is Low — And How to Fix It.
Spam filtering models don’t rely on “trigger words” anymore. Gmail isn’t penalizing you for saying “free” or “discount.” What it does pay attention to is whether your emails resemble known patterns from past junk mail.
That includes:
If your emails fit a pattern that filters have repeatedly classified as low-quality, they get grouped accordingly. This is why copying “proven cold email scripts” rarely works at scale.
Related reads: How spam filters work (& how to differentiate with cold emailing) and 12 Reasons Why Your Cold Emails Go to Spam.
Your domain’s overall behavior affects deliverability more than most people realize.
A domain used for newsletters, cold email, customer support, and CRM automation all at once creates mixed signals. Gmail and Outlook evaluate all of it together.
Most experienced senders separate things:
It’s cleaner for providers and far easier to scale without unintended penalties.
For more on this: The Top Email Blacklists That Wreck Cold Outreach.
Even though both evaluate similar categories, their weighting is different.
Gmail leans heavily on engagement and content structure. If replies slow down, or if templates look recycled, Gmail reacts quickly. It’s also more sensitive to patterns that resemble bulk automation.
Outlook is stricter about volume control and authentication issues. It tends to soft-block senders (often silently) when volume jumps too quickly or when identity signals aren’t fully aligned.
Understanding these differences helps you troubleshoot the right problem instead of guessing.
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There’s no trick to deliverability. The senders who inbox consistently are the ones who look legitimate.
That means warming up properly, keeping sending patterns predictable, avoiding template recycling, and paying attention to how recipients interact with your mail. It also means avoiding sudden changes in volume or timing.
Once your domain behaves like a trustworthy sender, inbox placement usually follows. When your patterns drift toward automation or inconsistency, filters adjust quickly.
Warmup matters because it gives inbox providers a clean, predictable baseline before you introduce anything risky.
The easiest way to get responses to your cold emails.
