Deliverability
Sender reputation
A score mailbox providers maintain for a sending domain or IP based on engagement, complaints and bounces, which determines whether your mail reaches the inbox, spam, or gets rejected outright.
What builds (and burns) reputation
Mailbox providers watch how recipients react to your mail and how clean your sending is. No provider publishes its exact formula, but the signals are well understood.
- Complaint rate, the share of recipients who mark your mail as spam. Keep it well under 0.1%. Gmail treats 0.3% as a hard limit for bulk senders.
- Bounce rate. A high hard-bounce rate signals a bought, old or scraped list.
- Engagement: opens, clicks, replies, and moving mail out of spam.
- Spam trap hits and blocklist listings.
- Consistency. Sudden spikes in volume look like a compromised account.
Domain vs. IP reputation
Providers track both. IP reputation used to dominate, but domain reputation now carries most of the weight, because it follows you when you switch IPs or providers. That’s why authenticating with your own domain matters: you’re building reputation you own.
How to recover a damaged reputation
Stop sending to unengaged contacts, remove bounced addresses, and send only your most wanted mail, such as transactional email and recent, engaged subscribers, until the numbers settle. Tools like Google Postmaster Tools show how Gmail sees your domain.
Reputation in MailCraft
MailCraft tracks your bounce and complaint rates over a rolling window and rates your reputation as good, warning or at risk, in the dashboard and through the API. Hard bounces and complaints are suppressed automatically, so the same mistake can’t hurt you twice.
Let MailCraft handle the details
Authentication, bounces, complaints and suppression are built in. Start free with 3,000 emails a month, no credit card required.
Start freeRelated terms
Full glossaryDeliverability
Engagement rate
How often recipients open, click, or otherwise interact with your email — a primary signal mailbox providers use to decide future inbox placement.
Sending & delivery events
Complaint (FBL / feedback loop)
A signal from a mailbox provider that a recipient marked your email as spam. Feedback loops relay these back to senders so the address can be suppressed.
Deliverability
Blocklist (or blacklist)
A list of IPs or domains flagged as sources of spam or abuse, checked by many receiving servers before accepting mail — landing on one can tank deliverability until you’re delisted.