How cold email actually works, written down properly.
Authentication, unsubscribe standards, provider policy and the law — with the RFC or the vendor page that says so, linked. No statistics we cannot source.
Why out-of-office replies don't reach your tool
RFC 3834 sends automatic replies to the envelope return path, not to Reply-To. A tool that routes replies by rewriting Reply-To never sees the conformant ones.
RFC 3834Auto-repliesSMTPReply handlingDeliverability9 minBulk sender rules: Google, Yahoo and Microsoft
The exact 2024 Google and Yahoo sender requirements plus Microsoft Outlook.com from May 2025 — thresholds, the 0.30% spam rate, and who each rule binds.
DeliverabilityGmailYahooOutlook.comDMARC9 minDetect a company’s email provider from DNS
MX records name the mail provider — until a security gateway hides it. Read the signatures, then fall through to autodiscover, SPF and DKIM selectors.
DNSMX recordsMicrosoft 365Google WorkspaceDeliverability8 minMicrosoft 365 DKIM: the onmicrosoft.com d= problem
Microsoft 365 does not sign custom-domain mail with your custom domain until you turn DKIM on. Why that breaks DMARC alignment, and the two CNAMEs that fix it.
dkimdmarcmicrosoft-365dnsdeliverability9 minGmail API scopes: request gmail.send, nothing more
gmail.send is a sensitive scope: verification only. gmail.readonly, gmail.compose, gmail.modify and mail.google.com are restricted and need a CASA audit.
OAuthGmail APIMicrosoft GraphVerification9 minMailbox warm-up: what actually matters
Sender reputation is built from sending activity, not elapsed time. What Google, Microsoft and M3AAWG document about warm-up — and the mistake most ramps make.
DeliverabilityWarm-upSender reputationCold email9 minRFC 8058 one-click unsubscribe, done right
One-click unsubscribe needs two DKIM-signed headers and an endpoint where GET changes nothing. Get that backwards and link scanners unsubscribe your list.
DeliverabilityRFC 8058UnsubscribeCAN-SPAM8 minSend time should follow the recipient’s clock
How to schedule outbound email in the recipient’s local time: resolving an IANA zone from country and city, validating it, and computing hours with Intl.
Send schedulingTime zonesIANA tzdbCold emailJavaScript9 minWhat UK law allows for B2B cold email
PECR’s email consent rule only bites on individual subscribers, so a limited company needs no consent. UK GDPR still applies in full to the named human.
UK GDPRPECRComplianceCold emailICO10 minWhy shared ESPs ban cold email
Every transactional email provider's AUP forbids unsolicited bulk mail. Quoted verbatim from Twilio, Mailgun, Postmark, Resend and AWS, with what to do instead.
DeliverabilityCold emailESP policyCAN-SPAM9 min