Apollo.io
ZoomInfo
Lusha
Hunter.io
Instantly.ai
Clearbit
Snov.io
lemlist
InboxStack
GlockApps
Email Testing By Inbox Pirates
Validity LLC
MxToolBox
Folderly
HetrixTools
Inbox AI
InboxStack is an email deliverability intelligence platform built for teams who need to know why their emails aren't reaching the inbox โ not just that they aren't. At its core is Brain, a proprietary causal AI engine trained on a 22-year deliverability knowledge base, which correlates signals across your ESP, DNS authentication records (SPF, DKIM, DMARC), Google Postmaster Tools, Microsoft SNDS, and 50+ blocklists to pinpoint root causes instead of surfacing raw metrics.
Most deliverability tools stop at monitoring: they show you a drop in inbox placement or a blocklist hit and leave you to investigate. InboxStack goes further, tracing the actual causal chain โ a DKIM misalignment, a reputation dip on a specific sending IP, a content trigger โ so you can fix the real problem instead of guessing.
Setup takes minutes with no migration required: forward your email headers for an instant DNS/authentication audit, or connect your existing ESP and Postmaster accounts for ongoing monitoring. Optional seed testing gives you real inbox-vs-spam placement data across major providers.
Built for agencies managing multiple client domains and growing companies who've outgrown basic authentication checkers, InboxStack turns deliverability from a black box into a diagnosable, fixable system.
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We use Apollo with our Sales and BDR team to manage our cold outreach. The strength of the platform is the sequences and cadences that you can set up. Compared to other tools we have used in the past like Salesloft the UI is much easier to navigate. The main limitation is that the quality of data isn't as vast and often I can find prospects on Linkedin but not in Apollo.
Based on our record, Apollo.io seems to be more popular. It has been mentiond 69 times since March 2021. We are tracking product recommendations and mentions on various public social media platforms and blogs. They can help you identify which product is more popular and what people think of it.
Personal email domains destroy this. Clearbit's Enrichment API returns a null company when it hits gmail.com. Apollo routes personal domains straight to a consumer bucket and skips B2B fields entirely. Even PDL's /person/enrich endpoint โ the most permissive of the major providers โ gives you around 32% hit rate on Gmail addresses versus 74% on corporate domains. I measured this across 6,200 signups for a... - Source: dev.to / 2 months ago
A few things worth flagging: PDL beats Clearbit's historical rates for US and Western European companies, but drops to ~52% match rate for Japan and South Korea specifically. Apollo underperforms on raw company matching but returns significantly more contacts per domain in Prospector-style queries than Clearbit's Prospector ever did โ the tradeoff is more stale titles in the result set. Hunter.io is fast and cheap... - Source: dev.to / 2 months ago
One thing comparison guides consistently get wrong: Clay is not an enrichment API. It's a waterfall orchestration tool that calls People Data Labs, Apollo, Clearbit, and others in sequence for you. It's useful, but it adds 2โ8 seconds of latency per row in my runs and costs more per match than going direct. For a CRM webhook flow where you need sub-second enrichment calls, Clay is the wrong layer to hit first. - Source: dev.to / 3 months ago
Last year I ran the same LinkedIn Sales Navigator export through three enrichment APIs. Apollo matched 61% of the emails. Hunter.io matched 54%. An OSINT-first pipeline I'd built in n8n โ pulling from public sources before hitting any paid API โ matched 79% and cost roughly $0.003 per contact. The delta wasn't magic. It was sequence. - Source: dev.to / 3 months ago
Despite having its LinkedIn Page removed in 2025, Apollo remains a functional enrichment and outreach platform with 275M+ contacts. The free tier includes 10,000 credits and the $49/month basic plan is the cheapest entry point for a combined enrichment-plus-sequencing workflow. Apollo's data collection methods have attracted LinkedIn's attention, but the product continues to operate. The risk I'd assign it:... - Source: dev.to / 3 months ago
ZoomInfo - ZoomInfo is a B2B database providing detailed business information on people and companies.
GlockApps - G-Lock Apps is an interesting tool that might seem simple to some, but is quite essential to most online marketers.
Lusha - Search less. Sell more.
Email Testing By Inbox Pirates - Preview, Analyze & Test emails with one click.
Hunter.io - Find all the email addresses related to a domain
Validity LLC - Founded in 2010, located in Essex Countyโs City of Orange, NJ, and serving all 50 states of the U.S., Validity, LLC is considered a โOne Stop Shopโ for ...