Guide

Deliverability and authentication checklist

Mailbox providers now treat authentication and one-click unsubscribe as requirements for bulk senders, not extras. Use this checklist when you stay or switch. It does not replace each provider’s current policy page.

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1. Authenticate the domain you send from

• SPF — a DNS TXT record that lists which servers may send mail for your domain.
• DKIM — a cryptographic signature so receiving servers can tell a message was authorized and not altered.
• DMARC — a DNS policy that tells receivers what to do if SPF or DKIM fail, and that ties those checks to your From domain (alignment). Gmail and Yahoo ask bulk senders for a DMARC policy of at least p=none to start; tightening to quarantine or reject comes after you have clean reports.

Publish these on the domain in your From address, not only on a vendor shared domain. After a migration, wait for DNS to propagate and send a test to Gmail, Outlook, and Yahoo before the first full-list issue.

2. One-click unsubscribe

Gmail and Yahoo require a visible unsubscribe link in the body of marketing or subscribed mail, and a one-click unsubscribe path using the List-Unsubscribe and List-Unsubscribe-Post headers (the RFC 8058 method). Honor those requests quickly — the sender guidelines say within two days, and faster is better. Do not bury the link or require a login to opt out.

3. Gmail, Yahoo, and Microsoft rules (bulk senders)

• Gmail — official “Email sender guidelines” require SPF, DKIM, DMARC alignment, one-click unsubscribe for bulk senders, and a spam complaint rate that stays well below 0.3% (Google recommends staying under 0.1% and avoiding 0.3%). Start at Gmail’s sender guidelines.
• Yahoo — similar authentication, alignment, and one-click unsubscribe expectations for bulk senders. See Yahoo Sender Hub best practices.
• Microsoft / Outlook.com — high-volume requirements (authentication including aligned DMARC) have applied to senders above 5,000 Outlook.com messages a day, with a stated effective date of 5 May 2025. Read the current policy at Outlook Postmaster policies and Microsoft’s bulk-sender requirements summary.

4. Switching-day checklist

1. Pick the sending domain and add the platform’s SPF include, DKIM keys, and a DMARC record before you import.
2. Confirm the platform is placing List-Unsubscribe headers on campaigns (most major newsletter tools do this on modern plans; verify with a test message and the raw headers).
3. Export unsubscribes and bounces from the old tool and suppress them in the new one so you do not re-mail people who already left.
4. Warm up if you are moving from a shared domain or a cold custom domain: start with recent engaged readers, then expand.
5. Watch complaint and bounce rates for the first few sends. Pause and clean if complaints spike.

This is operational advice, not legal advice. Provider thresholds change; re-read the official pages when you migrate.