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Deliverability

Gmail, Yahoo and Outlook sender rules, in plain English

What the three biggest inboxes require from anyone sending marketing email in 2026, and what it means for a peptide brand's setup.

5 min read · November 2026
GuideWhich email platforms allow peptide brands?What 15 platforms' own policies say about peptides, with links to every one.
All field notes

Gmail and Yahoo started enforcing sender rules in February 2024, and Outlook followed in May 2025. Most of it is setup you do once. Skip it and your email gets rejected before anyone sees it, no matter how good the campaign is.

What every sender needs

  • SPF or DKIM on the domain you send from. Both is better.
  • Valid forward and reverse DNS for the sending servers, and TLS for the connection.
  • A spam complaint rate in Google Postmaster Tools under 0.3%, and ideally under 0.1%.
  • Properly formatted messages, which any real sending platform handles for you.

What bulk senders need on top

Gmail treats you as a bulk sender once you send close to 5,000 messages a day to personal Gmail addresses, and that status is permanent. Outlook uses the same 5,000-a-day line. Yahoo doesn't publish a number, so plan as if the rules apply to you.

  • SPF and DKIM both, plus a DMARC record. A DMARC policy of p=none is enough to start.
  • Your From address has to line up with the domain that passes SPF or DKIM.
  • One-click unsubscribe in the email headers, plus a visible unsubscribe link in the email.
  • Unsubscribes honored within two days.

What happens if you skip it

Google stepped up enforcement in November 2025: mail that doesn't meet the rules gets temporary or permanent rejections. Outlook rejects bulk mail that fails SPF, DKIM or DMARC from May 2025. If your spam rate goes over 0.3% at Gmail, it has to stay under that line for seven straight days before Google will help with delivery problems.

What it means for a peptide brand

  • Send from a subdomain like send.yourbrand.com with SPF, DKIM and DMARC published before the first send.
  • Make sure every marketing email carries one-click unsubscribe. TellySend adds it to every send, so Gmail and Apple Mail show their own Unsubscribe button next to your name.
  • Keep complaints low by mailing people who want to hear from you: send to recent buyers and openers first, and space emails out so nobody gets three in a day.
  • Watch Google Postmaster Tools for your sending domain, so you see a complaint spike before it costs you the inbox.

Sources

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