What is Blocklist?
A blocklist (previously called blacklist) is a database of IP addresses, domains, or senders identified as sources of spam, resulting in their emails being blocked or filtered.
A blocklist is a database of IP addresses, domains, or email addresses that have been identified as spam sources. When your sending IP or domain appears on a blocklist, inbox providers may reject your emails outright or route them directly to spam.
There are several types of blocklists:
**Public DNS blocklists (DNSBLs)**: Maintained by organizations like Spamhaus, Barracuda, and SORBS. Inbox providers query these lists to check senders. Getting listed on Spamhaus can devastate deliverability across most major inbox providers.
**Private blocklists**: Individual inbox providers maintain their own internal blocklists based on spam complaints, spam traps, and sending patterns. These aren't public but affect delivery to their users.
**Enterprise blocklists**: Corporate IT teams maintain organization-specific blocklists to filter unwanted senders.
You can get blocklisted for: sending to spam traps, high complaint rates, sending to too many invalid addresses, sending malware, or being on a shared IP with bad senders. Removal (delisting) typically requires fixing the underlying problem and submitting a request to the blocklist operator.
Why Blocklist Matters
Blocklisting can instantly cripple your email program. If you're listed on Spamhaus, for example, the majority of your emails simply won't be delivered. Even minor blocklists can affect significant portions of your deliverability. The worst part: you might not know you're blocklisted until you notice deliverability tanking. Regular blocklist monitoring is essential for any serious email sender. Prevention—through list hygiene, authentication, and complaint management—is far easier than removal.
How Ark Handles Blocklist
Ark actively monitors our sending infrastructure against major blocklists. Because we enforce strict sending policies and immediately suppress bounces and complaints, our IPs maintain clean reputations. If you're on a dedicated IP and encounter blocklist issues, our deliverability team helps diagnose the cause and navigate the delisting process.
Frequently Asked Questions
How do I check if I'm on a blocklist?
Use free tools like MXToolbox, MultiRBL, or Spamhaus lookup to check your sending IP and domain against major blocklists. Check regularly—being blocklisted can happen suddenly and without notification.
How do I get removed from a blocklist?
First, fix the problem that got you listed (spam trap hits, high complaints, etc.). Then visit the blocklist operator's website and submit a delisting request. Most require you to explain what caused the issue and what you've done to fix it. Removal times vary from immediate to several weeks.
Which blocklists matter most?
Spamhaus (SBL, XBL, PBL) is the most impactful—most major inbox providers use it. Barracuda, SORBS, and SpamCop also have significant reach. Getting listed on any of these will noticeably impact deliverability.
Can I be blocklisted even with good practices?
If you're on a shared IP, another sender's bad behavior could get the IP blocklisted, affecting you. This is one argument for dedicated IPs at higher volumes. Also, purchased or scraped lists often contain spam traps that lead to blocklisting.
How long does it take to get delisted?
It depends on the blocklist. Some offer automatic expiration after 24-48 hours if no further issues occur. Others require manual delisting requests and review, which can take days to weeks. Spamhaus typically requires demonstrating that you've fixed the underlying issue.
Is 'blocklist' the same as 'blacklist'?
Yes, they mean the same thing. The industry has shifted toward 'blocklist' as more inclusive terminology. You'll still see 'blacklist' in older documentation and some blocklist service names.
Related Terms
Allowlist
An allowlist (previously called whitelist) is a list of approved senders whose emails bypass spam fi...
Spam Trap
A spam trap is an email address used to identify spammers, either recycled from abandoned accounts o...
Email Deliverability
Email deliverability is the ability to successfully deliver emails to recipients' inboxes rather tha...
IP Warmup
IP warmup is the process of gradually increasing email volume from a new IP address to build sender ...
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