Think of your email sender reputation as a hidden credit score that mailbox providers like Gmail, Microsoft Outlook, and Yahoo assign to your sending setup. When your score is high, mailbox providers trust your business and deliver your sales and marketing campaigns straight to your contacts' inboxes. When your score drops, providers filter your campaigns into spam or reject them completely.
To learn more about the fundamentals, read our guide on “What is Email Sender Reputation”.
Domain reputation: Attached to your brand domain name (such as @yourcompany.com). Mailbox providers evaluate how contacts react to campaigns sent under your domain. This score follows your brand even if you switch email platforms or sending servers.
IP reputation: Attached to the specific sending computer address (IP address) transmitting your emails. It measures whether that specific server sends steady, reliable email traffic over time.
Mailbox providers recalculate your domain and IP reputation behind the scenes using key performance signals:
Spam Complaint Rate: The percentage of recipients who click "Report spam". Keep this rate under 0.1% (fewer than 1 report for every 1,000 sent emails). If your complaint rate reaches 0.3%, providers will send your marketing campaigns directly to the spam folder.
Spam Traps: Hidden addresses used by email providers to identify senders with poor list quality.
Pristine traps: Addresses created solely to catch scrapers. They have never belonged to a real person and never opted in to receive marketing communications.
Recycled traps: Old, abandoned addresses that mailbox providers turned into traps to see if you continue sending campaigns to inactive contacts.
Hard Bounce Rates: The percentage of emails that fail permanently because the address does not exist or was closed. High bounce rates signal that your contact lists are outdated.
Negative vs. Positive Engagement: When contacts open your campaigns, mark your emails as safe, or pull them out of the spam folder, your score rises. When contacts delete your campaigns without opening them or flag them as spam, your reputation drops.
Use external diagnostic tools to evaluate how major mailbox providers score your sending domain.
Connect your domain to Google Postmaster Tools to track your domain reputation, IP reputation, and daily spam complaint rate among Gmail recipients.
Use Microsoft SNDS to review how Outlook, Hotmail, and Live evaluate your sending IP address. This tool tracks daily campaign volume, complaint rates, and whether your server has been flagged by Microsoft filters.
Run periodic checks on public blocklist databases to verify that your domain or IP is not listed on services like Spamhaus, Barracuda, or SpamCop. If your domain is listed, the database will provide specific steps to resolve the issue and request removal.
