If you’ve experienced this, you’re definitely not alone. I hear from people almost every week with the same concern: a message is accepted and lands in one inbox, while another mailbox routes it to the Junk folder. It feels arbitrary, but there’s a real explanation. Spam filters evaluate a mix of technical signals and recipient behavior. Small gaps in authentication, domain history, link patterns, or engagement can tip placement outcomes.
If one mailbox trusts my emails, shouldn’t the others as well?I wish things were that straightforward.
Let’s break down why this happens and outline the practical steps you can take to fix it. I’ll also explain the importance of warming up your domain, including when targeting Microsoft 365/Outlook recipients.
Spam filtering systems analyze several factors such as sender reputation, message content, and user interactions. Key influences include:
The upshot? You might appear trustworthy and pass standard checks yet still be treated as higher risk in some mailboxes, especially when sending from a newer domain or a shared IP address.
Certain issues frequently cause your mail to be flagged as Junk, even if it appears to land elsewhere:
d= domain or the domain used in SPF checks, filters treat the message as higher risk.Need a more detailed checklist for Microsoft environments? Check out this article on why Outlook sends emails to spam and how to fix it.
Before you move on to anything else, ensure that SPF, DKIM, and DMARC are set up correctly and that alignment is in place. Its not just about passing these checks, it’s about passing with the right alignment.
p=none policy to collect reports, then switch to a stricter policy when you’re confident your setup is stable.If you’d like a straightforward explanation, read this guide on SPF, DKIM, and DMARC explained in simple terms. It covers alignment without unnecessary jargon.
Think of sender reputation like a credit score built from many signals: how recipients interact with your messages, complaint rates, bounces, and the soundness of your technical setup.
This is where warming up your domain becomes invaluable. You need consistent, positive activity over time. The clearest signal? Real engagement: opened emails, replies, and messages that users rescue from spam folders.
Mailwarm is a tool that builds this foundation for you. It links your mailbox to a network of over a thousand active mailboxes, then sends low-risk, technically sound emails solely for the sake of reputation building. The network’s mailboxes open, reply to, remove from spam, and even tag your emails as Primary where appropriate. These real, automated interactions signal trustworthiness to modern filtering systems.
As your sending reputation improves, you’ll see lower spam scores and more emails landing in the inbox. Warm-up often yields noticeable improvements in stricter, enterprise-focused environments.
Combine these practical steps with a solid warm-up routine for maximum improvement with Microsoft:
If you’re still finding Outlook places emails in Junk, refer back to the more comprehensive Microsoft-specific guide for troubleshooting more complex scenarios.
Mailbox providers are ever quicker in flagging patterns they deem risky. Sending from new domains, new IPs, or having irregular sending frequencies is enough to raise red flags. Warm up provides the consistent sender history that email filters require to build trust in your messages.
With Mailwarm, this process is automated. Your mailbox engages with a real, managed network, ensuring emails are opened, replied to, or rescued from spam folders as appropriate. This genuine-looking activity is, in fact, authentic, and steadily builds your sending reputation through positive engagement.
One last crucial point: Receiving a server response of “250 OK” just means your email was delivered successfully to the server. However, whether it arrives in your recipient’s inbox or gets diverted to the spam folder is a separate issue, called deliverability. The two are not the same, understanding the difference is vital for fixing real-world email problems. For more on this distinction, read this overview comparing deliverability and delivery.
Spam filters score and classify messages using many signals, which is why the same message can end up in different places. If your emails keep getting Junked, focus on fixing authentication alignment, using best-practice infrastructure, and building a steady history of positive engagement. Warm up plays an essential role here, especially with new or rarely used domains.
If you’d like an expert review of your setup, reach out to experienced deliverability consultants for feedback. Sometimes, a short review can save you weeks of troubleshooting. You can contact mailadept for tailored help.
Some filters apply stricter policy- and risk-based checks. Even if a message is accepted elsewhere, gaps in authentication, poor engagement, or domain history can still cause a Junk outcome.
Domain warming up builds a consistent sending reputation over time, crucial for gaining trust from email providers. Without it, youre risking your emails getting lost in the spam maze due to suspicious spikes in sending activity.
Absolutely, having strong alignment between SPF, DKIM, and DMARC ensures email authenticity and reduces the risk of being flagged as spam. It’s a non-negotiable step if youre serious about avoiding the junk folder.
No, engagement helps but it isn’t the only factor. Filters also weigh authentication, complaint rates, list hygiene, and sending consistency. Build strong, positive signals across your audience.
Avoid risky practices like using URL shorteners, sending from new domains without warm-up, and having inconsistent authentication settings. Ignoring these can quickly spell disaster for your deliverability.
Yes, using distinct domains and IPs for cold emails versus transactional ones helps safeguard your reputation. Mixing them increases the likelihood of all your emails being marked as spam due to different engagement levels and risk factors.
In many cases, reputational damage can be reversed through systematic warm-up and meticulous sending practices. However, if the domain is heavily blacklisted, starting with a fresh subdomain might be necessary.


