Email Sender Reputation: How Google and Microsoft Decide If You're a Spammer
By Puzzle Inbox Team · Apr 5, 2026 · 10 min read
Your sender reputation determines whether cold emails reach the inbox or land in spam. Here's how Google and Microsoft actually score you, and how to fix it.
Sender Reputation Is the Whole Game
Every cold email you send passes through a filter that decides one thing: does this email belong in the inbox or the spam folder? That decision is based almost entirely on your sender reputation, a score that email providers assign to your domain and, to a lesser extent, your sending IP address.
Think of sender reputation like a credit score for email. It takes time to build, it can drop fast with bad behavior, and once it's damaged, recovery is slow and painful. The difference between a "High" and "Low" reputation domain at Google is the difference between 95% inbox placement and 5% inbox placement. That's not an exaggeration. Reputation is the single most important factor in cold email deliverability.
Domain Reputation vs. IP Reputation
In the early days of email, IP reputation was king. Spam filters looked at the IP address an email was sent from and checked it against known spam sources. Block the IP, block the spam. Simple.
That changed as email sending moved to shared cloud infrastructure. Today, thousands of senders share the same IP ranges on Google Workspace, Microsoft 365, and services like SendGrid. Blocking an IP would block thousands of legitimate senders along with the spammers.
So email providers shifted to domain reputation. Your domain (the part after the @ in your email address) is now the primary identity that Google and Microsoft track. This means your reputation follows you regardless of which IP or infrastructure you use to send. You can't escape a bad domain reputation by switching providers. The reputation is attached to the domain itself.
IP reputation still matters in some contexts, particularly if you're using dedicated SMTP servers or sending through services with dedicated IP addresses. But for anyone using Google Workspace or Microsoft 365 for cold email, domain reputation is what determines your inbox placement.
The Signals That Build (or Destroy) Your Reputation
Bounce Rate: Keep It Under 2%
When you send an email to an address that doesn't exist, it bounces. Email providers track your bounce rate carefully because high bounce rates indicate that you're sending to unverified or purchased lists, which is a classic spammer behavior.
Google's threshold is strict: bounce rates above 2% will negatively impact your domain reputation. Above 5%, you're in serious trouble. For cold email, this means email verification isn't optional. Every single address on your list needs to be verified before it enters a campaign.
The fix is simple: use a quality email verification service and re-verify any list that's more than 30 days old. People change jobs, email addresses get deactivated, and what was valid last month might bounce today.
Complaint Rate: Keep It Under 0.1%
A "complaint" happens when a recipient clicks the "Report Spam" button in their email client. Google tracks this through its Feedback Loop, and the threshold is razor thin: above 0.1% complaint rate and your reputation starts taking hits. Above 0.3% and you're in critical territory.
To put that in perspective, if you send 1,000 emails, more than 1 spam complaint can start affecting your reputation. That's why targeting matters so much in cold email. When you email people who have no reason to hear from you, the complaint rate spikes. When you email people who genuinely might benefit from what you're offering, complaints stay near zero.
Spam Trap Hits: Zero Tolerance
Spam traps are email addresses operated by anti-spam organizations and email providers specifically to catch spammers. There are two types: pristine traps (addresses that were never used by a real person and were planted as bait) and recycled traps (old addresses that were abandoned and repurposed as traps).
Hitting even one spam trap can severely damage your domain reputation. Pristine trap hits are worse because they prove you're using a scraped or purchased list. Recycled trap hits indicate your list is outdated and unverified.
The only defense is rigorous list hygiene. Verify every email before sending. Remove addresses that bounce. Never buy pre-built email lists from vendors who can't verify their data sources.
Engagement: Replies Are the Strongest Positive Signal
This is the flip side of the reputation equation. While bounces, complaints, and spam traps damage reputation, positive engagement builds it. And the strongest positive signal is replies.
When someone replies to your email, it tells Google and Microsoft that your email was wanted and valuable. Reply rates of 2 to 5% tell email providers that your emails generate genuine conversations. This is why reply rate is the only metric worth tracking in cold email. It's not just a business metric. It's a deliverability metric.
Other positive engagement signals include: emails being moved from spam to inbox (the recipient rescued your email), emails being forwarded, and emails being starred or marked as important. But replies carry the most weight by far.
Google Postmaster Tools: Your Reputation Dashboard
Google Postmaster Tools is a free tool that shows you exactly how Google views your domain reputation. If you're sending cold email through Google Workspace, you should be checking this weekly. Here's what each metric means:
- Domain Reputation: Rated as High, Medium, Low, or Bad. High means your emails are landing in the inbox. Bad means they're going straight to spam. If you drop from High to Medium, reduce your sending volume immediately and investigate.
- Spam Rate: The percentage of your emails that recipients marked as spam. Keep this under 0.1%. If it's above 0.3%, stop sending and fix your targeting.
- IP Reputation: Less relevant for Google Workspace users (you share IPs with other senders), but worth monitoring if you see consistent "Low" ratings.
- Authentication: Shows whether your emails are passing SPF, DKIM, and DMARC checks. This should be 100%. If any authentication is failing, check your DNS configuration with our DNS checker.
- Encryption: Shows TLS encryption rates. Should be 100% for any modern email provider.
How Fast Reputation Drops (and How Slow It Recovers)
This is the asymmetry that catches most cold emailers off guard. Reputation can drop overnight. A single bad campaign, a batch of unverified emails, a spam trap hit, any of these can take your domain from "High" to "Low" in 24 to 48 hours.
Recovery, however, takes weeks to months. Google and Microsoft are cautious about restoring reputation because spammers would otherwise just pause, wait a day, and resume. The typical recovery timeline looks like this:
- Day 1 to 3: Identify the cause of the reputation drop. Stop sending all cold email from affected domains immediately.
- Day 3 to 7: Fix the underlying issue (list quality, copy, targeting, authentication).
- Week 2 to 3: Resume sending at very low volume (5 emails per inbox per day) with only verified, high-quality prospects. Focus on generating replies.
- Week 4 to 6: Gradually increase volume while monitoring reputation daily. If reputation improves to "Medium," continue the slow ramp.
- Week 6 to 12: Full recovery to "High" reputation, if you've maintained clean sending throughout. Some domains never fully recover and need to be retired.
The lesson is clear: prevention is far more effective than recovery. Maintaining good sending practices, verified lists, and reasonable volume is dramatically cheaper than trying to rehabilitate a burned domain.
Why Pre-Warmed Inboxes Start With Established Reputation
Brand new domains and inboxes start with no reputation, which is almost as bad as bad reputation. Email providers treat unknown senders with suspicion. Your first emails from a fresh domain will often land in spam simply because the provider doesn't know you yet.
Warming solves this by sending and receiving real emails (typically through automated warmup networks) over a period of 14+ days. These warmup emails generate positive signals: opens, replies, and inbox placement, that build your reputation from "unknown" to "neutral" to "positive."
Pre-warmed inboxes from a quality provider come with this warmup already completed. Your domain has 2+ weeks of positive sending history, established engagement patterns, and a reputation that email providers recognize as legitimate. That's the difference between spending your first two weeks sending to spam and spending them booking meetings.
Check your domain's current reputation and authentication setup with our DNS checker and blacklist checker before launching any campaign.