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.
How blocklists work
Organizations such as Spamhaus maintain lists of IPs and domains linked to spam, usually detected through spam traps and complaint data. Receiving servers query these lists in real time, and a listed sender can have its mail rejected or filtered across many providers at once.
Not all blocklists matter equally
There are hundreds of blocklists, but only a handful are widely used by major providers. A listing on an obscure list may have no visible effect, while a Spamhaus listing can stop delivery almost everywhere.
Getting delisted
- Find and fix the cause first: a bad list import, a compromised account, or a form without validation.
- Request removal through the blocklist’s own process. Most delist automatically once the problem stops.
- Expect a relisting, often with a longer penalty, if the behavior continues.
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Full glossaryDeliverability
Spam trap
An email address with no real owner, used by mailbox providers and blocklists to catch senders with poor list hygiene — sending to one is a strong negative signal.
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.
Deliverability
Dedicated IP
A sending IP address used only by your account, giving you full control over its reputation — as opposed to a shared IP, whose reputation depends on every sender using it.