Sender reputation is not a single number you can look up — it is a composite score that each major mailbox provider calculates independently based on your sending history with their users. Gmail's view of your reputation may differ from Outlook's, which may differ from Yahoo's, because they each see only the mail flowing to their own users.
A strong sender reputation gives your messages a head start: they pass through filtering with fewer friction points, land in the primary inbox tab (rather than promotions), and benefit from a reputation buffer that absorbs occasional volume spikes or content anomalies. A poor reputation means even well-crafted, wanted email ends up in spam.
Signals that affect sender reputation
Spam complaint rate is the most influential signal. When a Gmail user clicks 'Report spam' on your message, Google records a complaint against your sending domain. Maintain complaint rates below 0.1% of messages sent to Gmail. Above 0.3% triggers filtering. Google Postmaster Tools shows this rate if your domain sends more than ~200 messages per day to Gmail.
Bounce rate affects IP and domain reputation. Hard bounces (550 permanent failures — the address does not exist) signal that you are not maintaining your list. A sudden bounce spike after an import tells mailbox providers you bought or harvested a list. Keep hard bounces below 2%.
Engagement is increasingly weighted. High open rates, click rates, and 'move to inbox' actions signal that your recipients want your email. Low engagement — especially combined with a pattern of low opens followed by spam reports — signals that you are sending to disengaged or unwilling recipients.
Spam trap hits are severe. A spam trap is an email address maintained by a blocklist operator or mailbox provider that was never a real user account. Sending to a trap signals that you either harvested addresses, bought a list, or have very poor list hygiene. A single hit on a high-value 'pristine' trap can trigger immediate blocklist listings.
How to check sender reputation
Google Postmaster Tools (postmaster.google.com) shows domain and IP reputation for traffic to Gmail. Reputation is displayed as High, Medium, Low, or Bad. Low means most of your mail is going to spam. Bad means the domain is considered a source of spam.
Microsoft SNDS (postmaster.live.com) provides complaint rates and spam trap hit data for traffic to Outlook and Hotmail. Both are free — register your sending domain and confirm ownership with a DNS TXT record.
Blocklist checks are a fast proxy: if your IP or domain appears on Spamhaus, Barracuda, or SpamCop, your reputation at those providers' users has already degraded. The MailerMonk reputation scorecard combines blocklist checks, authentication status, and SMTP diagnostics into a single report.
Frequently asked questions
01How long does it take to build sender reputation for a new domain?
Building from zero typically takes 4–8 weeks of consistent, low-volume sending to engaged recipients. Start by sending to your most engaged contacts at low volume (50–100 messages per day), gradually increasing volume each week. The goal is to generate positive engagement signals (opens, clicks) at a high rate before the volume grows large enough to dilute those signals.
02How do I recover from a bad sender reputation?
Stop all sends, fix the root cause (clean the list, pause the high-complaint campaign, revoke compromised credentials), delist from blocklists, then resume at very low volume to your most engaged segment. Gmail and Outlook reputation scores recover over 7–14 days of clean sending. There is no shortcut — volume ramps that are too aggressive extend the recovery period.
03Does sender reputation transfer to a new domain?
No — a fresh domain starts with no reputation history. This is why switching domains to escape a bad reputation does not work; the new domain starts from zero, meaning it triggers heightened filtering for new senders, while the old domain's negative signals may follow if patterns are similar. The correct path is to rehabilitate the existing domain.
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