Email deliverability is the ability of your messages to successfully reach your recipients’ inboxes—instead of being blocked, sent to spam, or lost in transit. Deliverability depends on many factors, including your sender reputation, email content, domain alignment, and recipient engagement. To achieve good inbox placement, it’s essential to understand how internet service providers (ISPs) and mailbox providers (Gmail, Outlook, etc.) assess every incoming email to filter out unwanted or harmful messages.


Reputation

Your email sending reputation—assigned by inbox providers—is a key driver of deliverability. It affects how much email providers are willing to accept from you, whether your messages get blocked outright, and Inbox placement (whether they land in inboxes, promotions, or spam folders).

Your reputation functions like a credit score: it goes up or down based on the performance of your past emails.

What helps reputation

  • High engagement (e.g., opens, clicks, replies)
  • Clean, verified lists
  • Consistent email sending patterns

What hurts reputation

If your complaint or bounce rate is too high, your domain and IP reputation will suffer and potentially violate our Acceptable Use Policy & Code of Conduct. A bounce rate over 5% or a complaint rate over 0.08% is considered high and may result in mail blocking by providers. See Google’s Sender Guidelines for more details.

If you’re using OneSignal Email, view your stats at Settings > Email > Reputation. For third-party services (e.g., SendGrid, Mailchimp, Mailgun), use their dashboards to monitor complaints and bounces.

Email Reputation Dashboard

Due to Gmail restrictions, the “Reported as Spam Rate” does NOT account for complaints from Gmail recipients. In order to see your reported “Spam Rate” with Gmail, you must connect Google Postmaster Tools.


How to maintain good reputation

Remove unengaged recipients

Helps reduce complaints and bounces

Unengaged recipients are more likely to complain and become invalid. Implement a sunset policy for users who haven’t opened or clicked in the last 3 months or 4 messages. This reduces the chance of complaints and keeps your list clean.

Easily do this with a Journey that uses a “Wait until” node that prevents users from continuing if they have not opened or clicked a prior email. Tag them to exclude from further messages and/or delete them.

Remove invalid email addresses

Helps reduce bounces

Before importing email addresses to OneSignal, remove typos and inactive/invalid addresses like:

  • @gnail.com, @yagoo.com
  • Emails with no domain or malformed syntax like someone@.com and something@example

If migrating from another platform, use its Suppression List to avoid re-importing bad emails. You can upload Suppression List and/or delete users.

Email validation tools

Validation services help detect invalid addresses (though they don’t prevent spam complaints):

Once validated, follow our import guide to upload clean lists.

Only email recipients who knowingly agreed to receive marketing messages. Simply logging in with an email does not count as consent.

Implement a confirmed or double opt-in approach

Strongly recommended for reducing bounces and complaints

Double opt-in helps confirm email validity, ensures legal compliance, and boosts engagement:

  • Verifies consent for GDPR, CAN-SPAM, etc.
  • Filters out fake/typo’d addresses
  • Reduces complaint/bounce rates
  • Prevents abuse/list bombing

Warm up new domains or IPs

Reputation affects sending volume. If you’re sending from a new domain, subdomain, or IP, or suddenly increasing volume, use a gradual warm-up strategy to avoid rejections.

Learn more about Email Warm-Up


Key deliverability concepts

Unsubscribed

Users who opt out via the unsubscribe link in your emails. These users will be suppressed automatically to ensure compliance and protect your reputation.

When a recipient unsubscribes, it indicates a lack of interest or preference to disengage from future email interactions. As such, honoring unsubscribe requests promptly is essential for maintaining sender reputation, compliance with anti-spam regulations like the CAN-SPAM Act, and fostering positive recipient relationships.

Bounced

Emails that fail to deliver due to invalid addresses (usually they do not exist or are spelled incorrectly). Bounce data is stored in your Suppression List and also visible in Event Streams.

Failed

Emails that are temporarily undeliverable due to:

  • Misconfigured domain (e.g., DMARC/DKIM issues)
  • Full inbox
  • Low reputation or blocklisting

"Too Old" deferral messages from Gmail for Poor Reputation

Failures appear in Email Message Reports > Audience Activity and Event Streams.

Failures are not added to suppression lists.

Spam complained

When recipients mark your email as spam, it triggers a spam complaint aka “Spam Report”.

Yahoo Report Spam Button

Common reasons for complaints include:

  • Irrelevant content
  • Excessive frequency
  • Email recipients that did not opt-in

To maintain a positive sending reputation and avoid deliverability issues, it is important to minimize complaint rates. Regularly analyze feedback, adjust content strategies, and provide easy opt-out options to ensure a satisfactory email experience for recipients. Follow the above best practices to keep your complaints low.

These events are available in Event Streams.

Due to Gmail restrictions, Gmail users that mark your emails as spam can only be reported in Google Postmaster Tools.

Suppression list

A blocklist within your OneSignal app that prevents sending to emails that have bounced or marked as spam. Manage it via the Suppressions Guide.

Blocklists

External or ISP-managed lists of spammy or harmful IPs/domains. Being listed will cause deliverability problems. Use tools like Spamhaus to check your domain/IP status.

Spam traps

Spam traps are email addresses that are not actively used by real individuals but are set up by ISPs or anti-spam organizations to identify spammers. If you send emails to spam traps, it indicates poor list hygiene or acquisition practices and can severely damage your sending reputation.


Engagement metrics

Opened

Opens refer to the number of times recipients open your email messages. Tracking email opens provides insights into the effectiveness of your subject lines, targeting and sender identity. High open rates indicate good inbox placement and engagement from recipients.

Clicked

Clicks represent the number of times recipients interact with links within your email messages. Tracking clicks allows you to measure the engagement and effectiveness of your email content and call-to-action (CTA). High click-through rates indicate that your emails are resonating with recipients and driving desired actions. Since recipients must open emails before being able to click a link, clicks are a very strong indicator of engagement.


Inbox placement

Inbox placement refers to where your email messages are delivered within recipients’ email inboxes. Proper inbox placement ensures that your emails are seen by recipients in the correct context and increases the likelihood of engagement. Inbox placement can be categorized into different sections of the inbox, such as Primary, Promotions, or Spam folders.

Gmail Inbox Tabs

Primary

The Primary Tab typically where important and personal communications are received. Achieving primary inbox placement indicates good sender reputation and email relevance, increasing the likelihood of recipients engaging with your messages.

Promotions

The Promotions Tab refers to emails that are delivered to a separate tab within recipients’ inboxes, specifically designated for promotional or marketing emails. While still visible to recipients, emails in the Promotions tab may receive less immediate attention compared to those in the Primary inbox. Inbox Providers often use algorithms to determine which emails are categorized as promotions based on sender reputation and email content.

Spam

Spam inbox placement refers to emails that are filtered by Inbox Providers and delivered to recipients’ spam or junk folders. Emails categorized as spam may contain suspicious or unwanted content, trigger spam filters, or have low sender reputation.