Email SpamHow to Prevent Emails Going to Spam: 6 Proven Fixes for B2B Cold OutreachStruggling with cold emails going to spam? Learn 6 proven fixes to improve email deliverability, covering warmups, SPF/DKIM setup, spam tests, content tips, and more.
If your emails keep ending up in spam and you don’t know why, you’re not alone.
In 2023, global email volumes hit 381 billion—a 14% year-over-year surge. But more volume hasn’t meant more visibility. Engagement is dropping as inboxes hit saturation and marketers scramble to stand out.
But you’ve followed the advice, written a solid copy, and perhaps invested in expensive tools. You’ve even scrambled for quick fixes: list cleaners, format tweaks, or switching email tools.
Why are responses still flatlining?
That’s the reality for many B2B teams today. Email deliverability has become a high-stakes, low-visibility problem. One that quietly kills outreach performance and pipeline potential.
The issue isn’t just your subject line or your CTA. It’s deeper: poor sender reputation, misconfigured authentication, content that triggers filters, and a lack of engagement history.
And while the internet is full of tips, most are conflicting or too technical to act on.
This guide cuts through the noise. You’ll learn how to prevent emails from going to spam with six clear, proven fixes—no fluff, no gimmicks, just what works today.
When troubleshooting cold email deliverability, most people try the obvious: tweaking subject lines, rewriting copy, or changing CTAs.
But spam filters don’t rely on a single red flag. They score your emails on multiple signals: technical, behavioral, and content-related.
Here are the three biggest factors inbox providers use to evaluate your emails:
Now, let’s unpack each one.
Your sender reputation is like a credit score for your domain and IP address. Gmail, Outlook, and other providers track how recipients interact with your emails over time.
If your messages consistently get opened, replied to, or marked as important, your reputation improves. If they're ignored, deleted, or reported as spam, even by a small percentage, your reputation drops.
Reputation builds slowly and can be damaged quickly. That’s why new domains, cold inboxes, or inboxes with a history of complaints are especially vulnerable. Fixing reputation issues often requires rebuilding trust through a warmup process.
Most senders assume deliverability is all about content. It’s not, but content still plays a role.
Spam filters scan for certain patterns: overused keywords, links, attachments, odd formatting, or the presence of tracking pixels. Even legitimate emails can be flagged if they resemble messages commonly associated with spam.
For example, subject lines with weight loss, 100% free, or ALL CAPS trigger red flags, especially if the domain isn’t well-established. On the flip side, minimal plain-text emails that mimic human behavior tend to perform better, especially in cold outreach.
Your tech stack matters more than you think.
Spam filters don’t just read your content. They inspect the infrastructure behind it. That includes which provider you're using (Gmail Workspace, Outlook, SMTP relay, etc.), the IP address sending the mail, and whether your domain has proper DNS records like SPF, DKIM, and DMARC.
Even if you’re sending manually from Gmail or Outlook, a missing record or misconfigured ESP can cause your emails to be treated as unverified or suspicious.
Understanding why emails go to spam is only half the battle. The real challenge is knowing what to do next.
Below, we’ll walk through six proven fixes that help you regain control. Each one is grounded in how filters actually work, and includes what you can do on your own, plus where a tool like MailReach can help you go further.
Explore how Mailreach can help.
An inactive inbox is one of the fastest ways to get flagged by spam filters.
When you start sending emails from a new or inactive domain, Gmail and Outlook treat you with caution. Until your domain has a proven track record of engagement, your emails are more likely to be filtered, even if your message is strong and your list is clean.
You can warm up an inbox manually by sending a few personal emails each day, asking for replies, and gradually increasing your volume over time.
It works in theory, but it’s time-consuming, hard to scale, and nearly impossible to track across multiple inboxes.
It’s also easy to miss key signals—like whether your emails land in the Promotions tab instead of Primary. And manual warmup usually lacks the kind of varied, natural engagement (opens, replies, stars, spam recovery) that spam filters look for.
If you’re still looking to do this manually, here are some ways you can warm up your email domain in 2025.
Spam filters don’t just care how many emails you send. They care who’s engaging with them and whether that activity looks human.
Interactions from real Google Workspace and Office 365 inboxes carry more weight than activity from random SMTP servers or scripted tools, especially for B2B outreach. For B2C emails, it's also important to receive positive interactions from Gmail, Hotmail, and Outlook.
Some platforms promise features like “template warmup” or “industry-based content,” but filters don’t care about content style. They care only about authentic engagement signals.
Every MailReach warmup email mimics organic inbox behavior: it gets opened, replied to, starred, and even pulled out of spam. This builds a reputation you can trust before any cold outreach begins. Most of these interactions come from Google Workspace and Office 365, which makes it ideal for B2B emailing.
Try MailReach’s Email Warmup Tool.
If you want mailbox providers to trust your emails, authentication is foundational. Protocols like SPF, DKIM, and DMARC act as your domain’s proof of identity. They tell Gmail, Outlook, and others: “This email is actually from me, not a spoofed or malicious sender.”
Here’s what each one does:
You’ll need access to your domain’s DNS settings, and ideally someone on your team who understands how TXT records work. Most email service providers offer basic help with this.
MailReach offers free SPF and DKIM checkers that instantly show if your records are valid and properly implemented. It’s a fast way to make sure your technical setup is ready before your campaigns start scaling.
Run the SPF Checker for a free health check for your account. And get free reliable DKIM validation here.
Where your email goes — Primary, Promotions, Spam, or nowhere — is what matters. Even if your content is polished and your authentication is set up correctly, you won’t know how inbox providers are treating your emails unless you test for deliverability.
Spam filters evaluate both the technical setup and message content, including phrasing, formatting, links, and structure.
Cold emails are especially vulnerable, as they often come from unknown senders with limited engagement history. You’re being judged not just by what you say, but how closely it mimics spam behavior.
Even a legitimate campaign can get filtered out if it resembles spam.
Here are some content elements that commonly trigger filters, and safer alternatives to consider:
You can test deliverability manually by creating Gmail, Outlook, and Yahoo test accounts, sending yourself emails, and observing where they land. This might work for one message, but it doesn't scale, and it won't tell you why a message failed. And without feedback, it’s guesswork. You won’t know which part is causing issues.
To truly improve deliverability, you need deliverability testing that provides clear, actionable feedback across inbox types.
MailReach’s Spam Test sends your email to a controlled list of 30+ real inboxes across Gmail, Workspace, Outlook, Yahoo, and others, under live sending conditions.
You’ll see exactly where your email lands (Primary, Promotions, Spam), and get alerts via Slack or email if deliverability drops.
This turns inbox placement from a guessing game into a measurable workflow.
Inbox providers track how people interact with your emails. This engagement directly shapes your sender reputation and whether you reach the inbox.
Gmail, Outlook, and others look for:
Low engagement or high complaint rates, even from a small group, can send your emails to spam more consistently over time.
You can improve engagement with a few key adjustments:
Already using MailReach? Your engagement simulation takes care of this baseline, but your real audience still needs to care.
Sending too many emails too quickly from a new or untrusted inbox is a red flag. Inbox providers expect gradual, human-like activity. Even high-quality campaigns can hit spam folders if volume spikes too fast.
That’s especially critical for B2B cold outreach, where thresholds are much lower than B2C marketing.
Here’s a safe ramp-up plan for B2B cold email senders that we recommend:
Note: These limits apply only if you’re sending from Google Workspace or Microsoft 365 inboxes. If you’re using other providers (like SMTP relays), cap your volume at 50/day or less.
For B2C outreach, newsletters, and transactional emails, the number of emails you can send every day can go much higher.
MailReach warms up inboxes before you begin outreach, building a solid sending history. During campaigns, it continues simulating positive interactions, so if your real emails cause a small dip in reputation, MailReach helps balance it out.
This makes volume growth safer and more predictable, especially across multiple inboxes.
Nothing damages your reputation faster than spam complaints. Email bounces are not ideal for your reputation either, but still something you can work with, if you stay below a rate of 3-5%. If you use Mailreach, it would generate a lot of positive engagement, which makes it even easier to balance the bounces.
Bad data, like old addresses, role-based emails, and purchased lists, can drag down performance even if your content and setup are perfect.
Inbox providers take note when:
Build your list through opt-ins or targeted prospecting. Use a third-party verifier before launching a campaign, and regularly remove leads that haven’t opened or replied in weeks.
MailReach is built for teams that live and breathe cold email. If you’re running B2B outreach, whether you're a startup growth team, a lead gen agency managing 50 inboxes, or a recruiting firm sourcing candidates at scale, this is where MailReach performs best.
It’s designed to build sender reputation, validate your technical setup, and keep your emails out of spam at every stage of the workflow.
But it’s not the right tool for everything. If your focus is on B2C newsletters, transactional emails, or bulk promotions, MailReach won’t deliver what you need. These use cases rely on different infrastructure and metrics, and require a different kind of platform.
But for high-volume, high-stakes B2B outreach where inbox placement directly affects revenue? MailReach is the tool for you.
Explore MailReach in action → Watch the Demo
Deliverability issues rarely announce themselves. They quietly drain your reply rates, stall your pipeline, and shrink your revenue without obvious warning signs.
With MailReach, you get the tools to build reputation, detect problems early, and confidently send at scale.
👉 Start warming your inbox today
Warmup builds trust, but that trust can break fast. Spammy content, poor list hygiene, authentication gaps, or sudden volume spikes can undo your reputation, even if warmup was done right. You need to monitor all three pillars: sender reputation, content, and technical setup.
Most tools rely on custom SMTP inboxes or scripted templates. MailReach uses real Google Workspace and Microsoft 365 inboxes and simulates human-like behavior—opens, replies, and even spam recovery. That makes the warmup quality stronger, more realistic, and more reliable at scale.
Yes. MailReach is built for teams managing dozens or even hundreds of inboxes. You can apply custom schedules, monitor performance across accounts, and scale outreach without risking deliverability.
Every email in spam equals to a lost potential customer. Start improving your inbox placement today with MailReach spam testing and warmup.
Following the rules isn’t enough—know where your emails land and what’s holding them back. Check your spam score with our free test, and improve deliverability with MailReach warmup.
Without the right warmup, your best campaigns are of no use. You can start by first testing your inbox placement and begin improving it today.
How to Prevent Emails Going to Spam: 6 Proven Fixes for B2B Cold Outreach
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