April 6, 2026
What is Sender Reputation and How Does It Affect Deliverability?
Sender reputation is the score ISPs assign to your domain and IP. Understand what builds it, what damages it, and how to monitor yours.
Every time you send an email, the receiving server quietly evaluates you before deciding where to place your message - inbox, spam folder, or reject entirely. That evaluation is based largely on your sender reputation.
What is sender reputation?
Sender reputation is a trust score assigned to your sending domain and/or IP address by ISPs (Gmail, Outlook, Yahoo, etc.) and anti-spam networks. It's not a single public number - each provider calculates their own score based on signals they observe over time.
Think of it as a credit score for email. Build it carefully over time, and you get inbox placement. Damage it, and recovery can take months.
What signals affect your reputation?
Positive signals:
- Low bounce rate (below 2%)
- High open and click rates
- Subscribers adding you to their contacts
- Recipients moving your emails from spam to inbox
Negative signals:
- High bounce rate - you're sending to invalid addresses
- Spam complaints - recipients are marking you as spam
- Low engagement - emails are never opened
- Being listed on spam blacklists (Spamhaus, Barracuda, etc.)
- Sending to spam trap addresses
Domain reputation vs IP reputation
Modern ISPs weigh domain reputation more heavily than IP reputation. This means:
- Switching to a new IP won't reset a damaged domain's reputation
- A new domain starts with no reputation - you need to build it
- Subdomains inherit some, but not all, of the root domain's reputation
If you're planning a new email program, consider using a dedicated sending subdomain (e.g. mail.yourcompany.com) to isolate your transactional and marketing reputation.
How to monitor your sender reputation
Several free tools can give you visibility:
- Google Postmaster Tools - shows your domain reputation with Gmail as
High,Medium,Low, orBad - Microsoft SNDS - shows IP reputation for Outlook/Hotmail
- MXToolbox - checks if your domain or IP appears on major blacklists
Check these before and after large campaigns to catch problems early.
The fastest way to damage your reputation
The single fastest way to damage your sender reputation is sending to a large volume of invalid addresses. A bounce spike from a bad list import can drop your reputation from High to Low overnight with Gmail.
The fix is simple but needs to happen before you send, not after: verify your list.
Run a free bulk verification on your list at MailTruster before your next campaign.