Cold email deliverability: a sourced checklist for 2026

• Authenticate first. Google asks every sender to set up SPF or DKIM, and anyone sending more than 5,000 messages a day to Gmail to use SPF, DKIM and DMARC. A DMARC policy of p=none meets that.
• Warm each mailbox, then start cold sending low. Warmerly's warmup ramp runs 30 days, from 4 warmup messages a day to a ceiling of 50 (40 on Gmail, 30 on Outlook, 25 on Zoho).
• Keep your spam rate below 0.3% and aim for below 0.1%. That is Google's wording in Postmaster Tools. Yahoo says below 0.3%.
• Verify the list and stop on bounces. None of the three providers publishes a bounce limit, so set your own tripwire. Warmerly slows a mailbox from a 2% bounce rate and pauses sending at 7%.
• Watch Postmaster Tools, bounces and replies, not opens. Google says it does not track open rates, so a low open rate tells you little about spam placement.
• These rules do not mention cold email. Google's page says not to send to people who did not sign up and not to buy address lists. Cold outreach sits close to that line, so complaints matter more than any DNS record.

The three tables below are read from each company's own page on 24 October 2026. Where a page is unclear or contradicts itself, the cell says so.

What these pages do not tell you

• None of them is about cold email. They cover bulk and marketing mail. They do not say whether one-to-one cold outreach counts as marketing for the one-click unsubscribe rule. Many senders add the header anyway, and Warmerly does: campaign emails carry the RFC 8058 one-click pair when the mailbox has a link domain, and a mailto address when it does not.
• Under 5,000 a day does not mean exempt. Google's all-sender rules still apply to mail going to Gmail, and the spam filters act on complaints at any volume.
• Yahoo gives no volume threshold, so you cannot work out whether you count as bulk. Treat the bulk rules as the standard.
• Nobody publishes an inbox placement rate or a safe daily volume. Google tells senders to increase volume slowly and does not give a number. Any figure you read elsewhere is an estimate.

• Use a separate sending domain for cold outreach, not the domain your customers' mail comes from. This is practice rather than a provider rule: Google reports reputation by domain, so a bad week on your main domain reaches everything sent from it.
• Use a few mailboxes and spread the volume, instead of one mailbox at its limit. Mailboxes on one domain share the domain's reputation in Postmaster Tools, so more mailboxes spread the load but do not multiply a bad reputation into a good one.
• Keep the From: name and address consistent within a campaign, and use a Reply-To that can receive replies. Microsoft's post asks for a valid From or Reply-To address that can receive replies.
• Add an unsubscribe route. For cold email that means a one-line opt-out and a List-Unsubscribe header. Whoever opts out must stay out, and Yahoo asks senders to honour unsubscribes within 2 days.

A bad list is the fastest way to a bounce spike, and bounces are the number a campaign tool can measure directly. Microsoft's post asks senders to remove invalid addresses regularly and to manage bounces. Google asks senders not to buy addresses.

• Verify every address before sending: syntax, a live mail server for the domain, a mailbox check, and a test for catch-all domains that accept everything.
• Drop role addresses such as info@ and sales@ from cold lists. They reach shared inboxes, where a complaint costs the most.
• Never buy a list. Google's page says not to purchase email addresses from other companies.
• Suppress on bounce and on opt-out, across every campaign and mailbox, not only the one that bounced.
• Write to people for a reason. A message that is relevant to its reader gets fewer complaints, and the spam rate is the number Google, Yahoo and Warmerly's own limits all come back to.

No provider publishes a bounce limit, so the tripwire is yours to choose. Here is Warmerly's own, which is a product setting and not a provider rule. It uses a rolling 7-day window and needs at least 25 sends before it acts, because two bounces from ten sends is not a trend:

• Google Postmaster Tools reports your domain's spam rate, reputation, authentication and delivery errors for mail sent to Gmail. Check it weekly, and register the sending domain before warmup so there is a baseline.
• Spam rate: below 0.3% is Google's requirement and Yahoo's, and Google says to aim for below 0.10%. Yahoo calculates its figure from mail delivered to the inbox, so the same campaign can read differently in two systems.
• Bounces and deferrals: every campaign tool logs them. A rising trend is the earliest warning you have. See SMTP bounce codes explained.
• DMARC reports show every system sending as your domain, including ones you forgot. Read them for a few weeks before tightening the policy.
• Seed or placement tests show where a message lands, inbox or spam, at the providers you write to. They are a sample, not a promise.
• Replies, not opens. Google says it does not track open rates and cannot verify the accuracy of open rates reported by third parties, and that low open rates are not necessarily an accurate indicator of spam classification.

Warmerly shows where warmup mail landed, by provider, runs blocklist checks on your domains, and can run a placement test from your own mailbox on demand. See inbox placement and blocklist monitoring.

1. Day 1. Register or pick the sending domain. Publish SPF, DKIM and DMARC at p=none. Verify them with the checkers.
2. Day 1. Add the domain to Postmaster Tools and add a rua mailbox you will read.
3. Day 2. Create the mailboxes, connect them to your warmup tool, and start warmup. Do not send any campaign mail yet.
4. Days 3 to 7. Send a test message from each mailbox to a Gmail address you control and read the headers. Fix any failure before moving on.
5. Days 8 to 14. Verify the list. Write your tripwires. Prepare the sequence and the opt-out line.
6. From about day 14. If the readiness signals are steady, start campaigns at a small share of target volume and raise it after a clean week. Keep warmup running.

This is a plan to adapt, not a promise. Warmerly's ramp takes 30 days to reach a full warmup volume, so keep early campaign volume well below the mailbox's ceiling for the first month.

Every figure from another company on this page was read from that company's own page on the date shown. Pages change, so check the source before you rely on a number.

• Google, Email sender guidelines, read 24 October 2026
• Yahoo Sender Hub, best practices, read 24 October 2026
• Yahoo Sender Hub, FAQs, read 24 October 2026
• Microsoft, Outlook's new requirements for high-volume senders (2 April 2025, with the 29 April update), read 24 October 2026
• RFC 7208, Sender Policy Framework, read 24 October 2026