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Deliverability

Blocklist

A list of senders, IP addresses, or domains that are blocked from delivering email to certain recipients.

Definition

A blocklist (formerly called blacklist) is a real-time database of IP addresses, domains, or senders identified as spam sources. Email servers check incoming mail against blocklists and may reject or filter messages from listed senders. Being blocklisted severely impacts email deliverability.

Why It Matters

If your sending IP or domain lands on a major blocklist, your emails may be rejected by many receiving servers. This can devastate your email program. Regular monitoring and maintaining good sending practices helps prevent blocklisting.

How It Works

Organizations maintain blocklists based on spam reports, spam traps, and sending patterns. When you send email, receiving servers query these lists. If your IP or domain is listed, your email may be blocked or sent to spam. Each blocklist has its own criteria and removal process.

Best Practices

  • 1Monitor major blocklists regularly for your sending IPs and domains
  • 2Maintain clean lists to avoid spam traps
  • 3Act quickly if blocklisted - identify the cause and request removal
  • 4Use reputable ESPs with good IP reputation management

Frequently Asked Questions

Use blocklist checking tools like MXToolbox, Spamhaus Lookup, or your ESP's deliverability dashboard. These check your IP and domain against multiple blocklists. Check regularly as part of deliverability monitoring.

First, identify and fix the issue that caused the listing (spam trap hits, high complaints). Then follow the blocklist's delisting process, usually found on their website. Some lists remove automatically once the issue is resolved.