14 free tools
Deliverability
Meet the rules the big mailbox providers set before they start rejecting your mail.
The tools
Free deliverability tools: check what the bulk-sender requirements ask of a domain, see how a sending address is set up, and find what is getting mail treated as spam.
Bulk sender requirements checker
Check one domain against Google's and Yahoo's own published bulk-sender rules, with what neither can see named outright.
Live checkReverse DNS checker
Look up the PTR record for an IP address, and see what it is worth fixing for mail.
Live checkFCrDNS checker
Run the real two-hop forward-confirmed reverse DNS check on an IP address, not just the PTR half.
Live checkProvider sending limit checker
See Google Workspace's and Microsoft 365's own published sending limits side by side, each cited to the vendor's own page.
In your browserList-Unsubscribe header checker
Paste raw headers and see whether List-Unsubscribe and List-Unsubscribe-Post pass RFC 8058's one-click unsubscribe syntax, with no request ever sent to the link inside.
In your browserList-Unsubscribe header generator
Build the List-Unsubscribe and List-Unsubscribe-Post headers RFC 8058 one-click unsubscribe needs from your link, or nothing at all when the link cannot carry a POST.
In your browserTracking domain CNAME checker
Follow a tracking subdomain’s CNAME chain and see whether it ends at a known ESP’s tracking host.
Live checkMailbox calculator for cold email
How many mailboxes and domains a daily send target needs, once you say what one mailbox can safely carry.
In your browserWarm-up schedule planner
A day-by-day ramp from a starting volume to a target, at whatever daily growth rate you choose to plan around.
In your browserMailbox rotation planner
Split today's send evenly across an existing mailbox pool, and flag any mailbox pushed past the safe figure you set.
In your browserSpam trigger word checker
Check a subject and body against a fully shown list of urgency and money wording, all-caps words and repeated punctuation - grouped by category, nothing hidden.
In your browserSubject and preview text length tester
Count a subject line and preview text against the character cut-offs email service providers have actually measured, by client.
In your browserSPF/DKIM/DMARC alignment checker
Paste a message’s headers and see whether its DKIM signature and Return-Path actually align with the From: address the reader sees - strict and relaxed.
In your browserGmail message size clipping checker
Compare a message’s HTML, or a byte count you already have, against the ~102 KB estimate Mailchimp and Litmus each measured for Gmail clipping - never presented as Google’s own rule.
In your browser
More free tools
Every other family, and what it checks.
Email authentication
Check and build the SPF, DKIM and DMARC records that decide whether mail arrives.
22 toolsDNS
Read what a domain is really publishing, and build the records a provider asks for.
27 toolsDomains
See whether a name is free, who holds it, and what the registry says about it.
12 toolsFor developers
Try a webhook, a key or an API call without writing a script to do it first.
10 toolsMessaging
Work out what a text message really costs to send.
10 toolsPricing and billing
Work out what to charge, what it leaves you, and what a change mid-cycle costs.
17 tools
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