Monthly Archives: July 2025

Domain Reputation – Google’s Hidden Blocklist

Inbox Providers like Google, Yahoo! and Outlook.com are constantly evolving new ways to ensure that the email making their inboxes is safe, timely and relevant to their users. At their disposal are multiple layers of email technology protection:

  • TLS Encryption for connection
  • Blacklists (both internal and external)
  • DMARC Compliance (SPF Authentication, SPF Alignment, DKIM Alignment)
  • Spam Content Scoring Rules
  • Bulk Sender Spam Reporting Rules
  • Individual Spam/Junk Rules

In past blogs, we’ve discussed each of these layers, including Google’s Content Reputation checks. Today, we’ll discuss what we know about Google’s proprietary blocklists.

Blocklists come in two forms:

  1. A list of IP addresses that have sent spam or dangerous emails or should not be sending email at all.
  2. A list of Domains that have been used in fraud, phishing or spam emails.

Google employs both types of blocklist to limit the risk of spam email making their Inboxes. But, how does Google determine what IP addresses and domains to block?

Google’s Blocklist Logic

Traditional blocklists use a variety of methods to determine what IP addresses or Domains are threatening. Often these include networks of spam traps, honey pots and feedback from inbox owners. Google appears to leverage both commercially available IP blocklists and their own proprietary logic. Staying off a commercial blocklist is therefore the first step in making the Google inbox.

Google has access to more inbox data than any other Inbox Provider. They can leverage Customer Sentiment and Behavior to create an aggregate picture of incoming email from an IP address or domain. This works in a few ways:

  • Email from IP addresses that were marked as spam gives that IP address a negative reputation. Google tracks the ratio of those emails received to those marked as spam. Over a certain threshold, this sentiment causes the IP address to be blocklisted for all senders from that IP.
  • Email domains are similarly tracked across all inboxes. Over a certain threshold of users marketing the email as spam, all email from that domain will be marked as spam.
  • Email containing content that is similar to content from blocklisted IP addresses or domains is automatically placed in the spam folder.
  • Email domains with a persistent poor reputation maybe placed on a complete blocklist and fail delivery entirely.

How can you stay off Google’s Blocklists?

Staying off of Google’s Blocklists is similar to staying off any blacklist, with a few additional considerations:

  1. Maintain good email list hygiene. Remove old and unreactive email addresses to reduce the risk of being marked as spam.
  2. Use an email marketing service that spreads your sent email over multiple dedicated IP addresses for marketing campaigns. This reduces the risk of IP blacklisting.
  3. Do not use purchased email lists. These may contain aged, or spam trap inboxes or inboxes that have been filled. In addition, purchased lists are very low quality, increasing the risk that your email will be marked as spam and blacklisted.
  4. Use separate domains or subdomains for marketing, transactional and person-to-person email. This reduces the risk of your business email becoming blacklisted by a bad marketing campaign.
  5. Reduce the frequency of your marketing campaigns. Recipients are more likely to mark email as spam if they feel overwhelmed.

How do you recover your reputation?

If you have landed on Google’s Domain Blocklist, you have a difficult time ahead. All email may be completely refused or immediately sent to the Spam folder. Recovery takes time and patience. If you haven’t already, take the time to go through the steps listed above. Within a few weeks, you should see acceptance rates and open rates improve. If not, you have a more serious issue, Google has permanently blocked your Domain. Your only recourse may be to create a new domain from which to send email.

How does MxToolbox help?

MxToolbox Delivery Center provides the email delivery management and monitoring that you need to keep your messages flowing.

  • Monitor DMARC compliance rates across all senders
  • Closely monitor your Gmail Spam rate.
  • Check your email for 1-Click Unsubscribe, a requirement of Google and Yahoo! bulk sender rules
  • Analyze your campaigns for other potential reasons to miss the inbox with Inbox Placement 
  • Notify you of issues while they’re occurring to enable quick resolution and damage control

If this sounds complicated, MxToolbox also offers Managed Services team that can help you setup DMARC, DKIM, SPF, BIMI and get your domain aligned with Google’s bulk sender policies.

Content Reputation – Google’s Secret Sauce

Getting to a Google user’s inbox can be a complicated maze to navigate. Some of your emails arrive fine while others seem to hit only the Spam folder. The biggest factor is Google’s Bulk Sender Requirements. If you adhere to those rules, your email is most likely to make the Inbox. DMARC compliance, of course, is a base requirement.

But, what if you are still hitting the Spam folder?

Google is Judging Your Content

Remember that Inbox Providers are trying to provide a service to their customers. Part of this service is to improve the quality of their inbox experience by reducing spam emails and surfacing only email that their customers want to receive. Google categorizes emails in several ways:

  • Primary – Person-to-person email, direct business correspondence, etc.
  • Promotions – Newsletters, ad campaigns, sales circulars, etc.
  • Social – Notifications and invitations from social media platforms.
  • Transactional – Receipts, order confirmations, order updates, etc. Transactional can end up in Primary or Social.
  • Bulk – Email sent to a significant number of Google inboxes. Promotions are a bulk form of email.

As a marketer, you will want to land in the category most likely to get opened: Primary. However, Google and their customers want your email to be properly categorized so that they can prioritize their email. What folder or category your email ends up in is largely due to the content of the message!

What Content Gets You to the Spam folder?

Google is also judging your content versus other email content and user sentiment about those emails.

Google has four main reasons for marking your email as spam:

  1. Content is similar to other messages marked as spam.
  2. Content is similar to yours was used to steal personal information.
  3. Links in your email were suspicious.
  4. Emails from your Domain have been marked as spam in the past.

You can see the messaging Google uses in their web UI, in the screenshots below

What can you do if you have Content Reputation Issues?

The good news is that you control your content. You have the option to make changes to your emails before you hurt your domain reputation.

MxToolbox recommendations:

  1. Send separate and distinct emails for transactional and marketing purposes and do not mix marketing messages into a transactional email.
  2. Use distinct subdomains for Person-to-person, Transactional and Marketing emails. This will solidify the separation to Google and given their algorithm a clue into proper categorization.
  3. Review your Marketing lists regularly and prune outdated contacts in order to reduce the likelihood of your email being categorized as spam.
  4. Review your Marketing content for spammy/histrionic language.

How can MxToolbox help?

MxToolbox Delivery Center provides the email delivery management and monitoring that you need to keep your messages flowing.

  • Monitor DMARC compliance rates across all senders. DMARC is key to making the Google Inbox.
  • Closely monitor your Gmail Spam rate. Being reported as spam by a few senders will get you marked as spam in all Inboxes.
  • Check your email for 1-Click Unsubscribe, a requirement of Google, Outlook.com and Yahoo! bulk sender rules.
  • Analyze your campaigns for other potential reasons to miss the inbox with Inbox Placement. Our MxTips ™ give you insight into potential Content Reputation Issues by analyzing your campaigns before you send them.
  • Alert you to issues while they’re occurring to enable quick resolution and damage control.