Blacklist Checker

Instantly check an IP or domain against major email blacklists including Spamhaus, SURBL, SORBS, and more.


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CIDR to IP Range

Enter a CIDR notation to instantly convert it to an IP range.


Use CIDR to IP Range

SPF Analyzer

SPF is a method to prevent email sender address forgery. Enter your domain to analyze its SPF record.


Use SPF Analyzer


IP Range to CIDR

Enter a IP range to instantly convert it to a CIDR notation.


Use IP Range to CIDR

DMARC Wizard

Enter your domain to analyze your DMARC record or create a DMARC policy for your domain.


Use DMARC Wizard


DNS Lookup

Perform a DNS lookup against multiple widely used nameservers around the world.


Use DNS Lookup

Resources for #SeriousSenders


More than 90% of US and UK nonprofits and their email recipients are highly susceptible to fraud.

The latest installment in 250ok’s Domain-based Message Authentication, Reporting & Conformance (DMARC) adoption reports brings us some truly shocking and disturbing findings: Nearly 95% of US-based nonprofit organizations (NPOs) have no DMARC policy to protect their email recipients from fraud. We also analyzed UK-based NPOs and found they fared only marginally better, with almost 93% […]

Free your July 4th marketing emails from bad design!

We want YOU to send better marketing emails for your Fourth of July sales. Why? Because what’s more American than driving holiday revenue? Thus, we are back again with more help from MailCharts to bring you a 2017 look-back to inform your 2018 campaigns. Together we looked at 1007 emails mentioning variants of “July 4th” […]

The new email authentication frontier: Brand Indicators for Message Identification (BIMI).

Over the last decade or so, marketers have been hard at work implementing Sender Policy Framework (SPF) and DomainKeys Identified Mail (DKIM), and many have started down the road of implementing Domain-based Message Authentication, Reporting and Conformance (DMARC). But we never sleep on email, so we’re excited by the prospect of an additional frontier of […]




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