Sequencer fingerprints
Headers, tracking pixels and link domains left by sequencing tools such as Instantly, Smartlead, lemlist, Apollo, Outreach and Salesloft.
Keep cold email out of your team’s inbox
Most businesses do not send cold email. They receive it, more of it every month, written by agents that never tire of following up. inbound-guard tells you, and your agent, which incoming messages are automated outreach and why.
What it looks at
Cold outreach is sent the same way every time: from a spare domain, through a sequencing tool, in a series of nudges. Each of those leaves a trace in the message.
Look-alike sending domains
A spare domain like getacme.com or acmehq.io whose website just redirects to the real company. Senders keep their main domain clean that way.
Newly registered domains
The sending domain’s registration date, from public RDAP records. Cold domains are usually weeks old.
Follow-up patterns
“Just bumping this”, “circling back”, “worth a quick chat?”, and a Re: subject on a thread that never started.
Leaked merge fields
Placeholders like {{first_name}} or [Company] that a template failed to fill in.
First contact
A sender outside the contacts you give it, and replies sent to a different domain from the one it came from.
A score and the reasons
Every message gets a cold score from 0 to 100, a verdict (cold, likely cold or not cold) and the signals behind it. Use it in a mail rule, a script, or let your inbox agent decide what to do.
- CLI for a saved .eml file, an mbox export, or a message piped in. The exit code says cold or not.
- MCP server so an agent that reads your inbox can check a message before it answers, labels or forwards it.
- Library for your own mail pipeline.
$ npx @analyzemail/inbound-guard message.eml
COLD score 100
From [email protected]
Subject Quick question about your onboarding
Sent with a sequencing tool lemlist
New domain getacme.io registered 23 days ago
Look-alike sending domain getacme.io redirects to acme.com
Replies go to another domain replies to acme.com
Sales sequence wording "Worth a quick chat", "15 minutes"What it does not do
It does not move or delete mail
It gives a verdict. Whether a cold message is archived, labelled or answered is up to your rule or your agent.
It does not send your mail anywhere
Messages are read on your machine. The only lookups are DNS, RDAP and the website of the sender’s domain.
It does not judge the offer
A cold message can be one you want. The score says how it was sent, not whether it is worth reading.
It is not a spam filter
Phishing and malware are your mail provider’s job. inbound-guard is for the outreach that passes those filters.
Sending email instead?
If your team or your agent sends, check the list first. Every check Analyzemail runs, or the API and MCP server for agents.
Open source, MIT licensed, free to run.
inbound-guard needs no account. For checking lists you send to, create an Analyzemail account. Questions first? Email [email protected].