What happens when an IP gets blocklisted?
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When an IP hits a blocklist, mail from that IP starts getting blocked or filtered by every mailbox provider that consults that list. The blast radius depends on which blocklist fired.
The big ones matter most. A listing on Spamhaus SBL or XBL can effectively take you off the internet for hours, because a huge chunk of the mail ecosystem checks Spamhaus before accepting any connection. A listing on a niche list might only nudge you into the spam folder at a handful of providers. Proofpoint, Barracuda, and Cloudmark (now Proofpoint) feed enterprise filters and hurt B2B delivery specifically. So "blocklisted" isn't one thing, it's a spectrum.
The usual root causes are predictable. Complaint spikes from an aggressive campaign. A spam trap hit because a purchased or stale list slipped through. A compromised account sending real spam from inside the building. A sudden volume ramp that looks like abuse to the filters.
Your ESP's response is usually automatic. Traffic gets throttled off the affected IP. They file a delisting request with the blocklist operator, which is essentially "here's what we found, here's how we fixed it, please remove us." Some blocklists (Spamhaus, for example) take this seriously and want evidence of remediation. Others time out on their own after a cooling period if the signals clear.
What you should do in parallel, regardless of what your ESP is doing:
- Pause the campaign that triggered it, don't just let it keep firing.
- Pull the last 72 hours of sends and find the segment with the highest complaint or bounce rate.
- Clean the list. Remove anyone who hasn't engaged in the last 90 days before you resume.
- Double-check DMARC alignment and authentication. Compromises often expose auth gaps.
- Warm the recovered IP back up gradually. Don't jump straight back to full volume.
If you're on a shared pool, your ESP will handle most of this. If you're on dedicated, the rebuild is on you. Either way, if you want a fast sanity check on which blocklists you're actually on right now, Review My Emails runs a free multi-list check.
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