Cold email deliverability
Cold email deliverability is the share of your outbound cold emails that actually reach the recipient's inbox (not spam, not blocked). It depends on domain authentication (SPF, DKIM, DMARC), sender reputation, mailbox warmup, list hygiene and content — not just whether the email was 'sent'.
How it works
Mailbox providers score each sending domain and IP on engagement, complaint rate, authentication and volume patterns. Good scores land you in the inbox; bad ones route you to spam or block you outright.
Why it matters
A campaign with 'sent' status but 30% inbox placement is mostly invisible. Deliverability is the multiplier on every other metric — open, reply and meeting rates all collapse if placement is poor.
What should you check first when cold email replies suddenly drop?
Work from the cheapest check to the most expensive. Start with bounces. If the hard-bounce share on the last few sends jumped, a new list segment is the likely cause and nothing else needs investigating yet. Next, send a message to a test mailbox you control, open the raw headers and read the Authentication-Results line. It should show spf=pass, dkim=pass and dmarc=pass for your domain. A fail there usually traces back to a DNS edit, a newly added sending tool or a rotated key.
If authentication passes and bounces look normal, run a seed test to see which folder the message lands in at each provider. Only after that is it worth rewriting copy. Teams often reverse this order and spend a week on subject lines while the real fault is a broken record that the SPF, DKIM and DMARC checker would have shown in a minute.
How many sending mailboxes does a daily cold volume need?
Treat the per-mailbox cap as fixed and solve for the mailbox count. Suppose, hypothetically, you add 400 new prospects a day and each gets three emails over two weeks. Once the program is running, daily sends settle near 400 times three, or 1,200. At a cap of 40 sends per warmed mailbox, that needs 30 mailboxes. Doubling new prospects doubles the mailboxes; raising the cap per mailbox is the shortcut that burns reputation.
Spread those mailboxes over a few dedicated sending domains so a problem on one domain pauses a slice of the program instead of all of it. Google's February 2024 bulk-sender rules start at roughly 5,000 messages a day to Gmail accounts, counted across the sending domain rather than per mailbox, so a large program should plan for one-click unsubscribe and a spam rate held under 0.3%.
What does a healthy sent report fail to tell you?
A sent count confirms your tool handed messages to a server. A delivered count confirms the receiving server accepted them. Neither says which folder they landed in, and the folder decides whether anyone reads the email. Opens are a weak proxy as well: Apple Mail Privacy Protection loads tracking images on the reader's behalf, and some corporate security filters open links before a person does.
The numbers that move with real placement are replies, positive replies and complaints. If replies fall while opens stay flat, suspect the filter before the message, and compare against an inbox placement rate test from the same week to confirm it.
How is cold email deliverability different from newsletter deliverability?
A newsletter goes to people who asked for it, usually from an email service provider's infrastructure, and engagement from a warm audience carries the reputation. Cold email reaches strangers from ordinary Google Workspace or Microsoft 365 mailboxes, so the baseline of opens and replies is lower and each complaint weighs more. That is why cold programs lean on small volumes per mailbox, plain one-to-one formatting and strict list verification.
Autocloz handles the mechanics inside the sending account: DMARC, DKIM and SPF monitoring per domain, inbox-placement tests, a 21-day mailbox warmup ramp and sender rotation across mailboxes on paid plans. The Free plan covers up to 10 mailboxes with warmup and monitoring included, and placement tests show whether the setup is working before volume goes up.
How Autocloz handles it
Autocloz ships 21-day mailbox warmup, DMARC/DKIM/SPF monitoring and inbox-placement tests, plus per-domain rotation and sending caps — so placement is managed, not guessed.
Free tools for this
No signup required — they run in your browser.
FAQ
How do I improve cold email deliverability?
Authenticate your domain (SPF/DKIM/DMARC), warm up mailboxes for ~3 weeks, keep lists clean (verify before sending), rotate across mailboxes, and watch complaint + bounce rates. Autocloz automates the warmup + monitoring.
Does warmup actually help?
Warmup builds early engagement signals on a new domain/mailbox so providers trust it before you ramp volume. It's necessary but not sufficient — authentication and list hygiene matter just as much.
Related terms
DMARC (Domain-based Message Authentication, Reporting & Conformance) is an email standard that tells receiving mail servers what to do with messages that fail SPF or DKIM checks — and sends you reports. It prevents spoofing of your domain and is now effectively required by Gmail and Yahoo for bulk senders.
SPF (Sender Policy Framework) is an email-authentication standard that lets a domain owner publish, in DNS, the list of mail servers allowed to send email on the domain's behalf. Receiving servers check the sending IP against that list to help detect spoofing and decide whether to trust the message.
DKIM (DomainKeys Identified Mail) is an email-authentication method that attaches a cryptographic signature to each message. The receiving server verifies the signature against a public key in the sender's DNS, proving the message wasn't altered in transit and genuinely came from the signing domain.
Mailbox warmup is the practice of gradually increasing a new email account's sending volume while generating positive engagement (opens, replies, moving mail out of spam) so mailbox providers build trust in the sender before real campaigns ramp up.