Email sender requirements: Gmail, Yahoo and Outlook
Gmail and Yahoo have enforced sender rules since February 2024, and Outlook.com since May 2025. What each one requires, from its own pages, with the differences that trip senders up.
The rules side by side
“Bulk” means the provider’s own definition in the first row. Each cell links to the page it comes from.
| Requirement | Applies to | Gmail | Yahoo Mail | Outlook.com |
|---|---|---|---|---|
| Who counts as a bulk sender | definition | Close to 5,000 or more messages a day to personal Gmail accounts, counted per primary domain. Once reached, always bulk. Google | No number published: a “significant volume”, judged per authenticated or From domain. Yahoo | 5,000 or more messages a day to Outlook.com, Hotmail, Live.com, MSN and other Microsoft consumer addresses, all from one From domain. Microsoft Microsoft |
| SPF or DKIM | all senders | Required. Google | Required. Yahoo | Not stated for senders under the bulk line. |
| SPF and DKIM and DMARC | bulk senders | All three required. Google | All three required. Yahoo | SPF and DKIM must pass, and a DMARC record must be published and pass. Microsoft |
| DMARC policy | bulk senders | At least p=none. Google | At least p=none, and it must pass. Yahoo | Any valid policy, p=none included. Microsoft |
| Alignment | bulk senders | From: domain aligned with the SPF or the DKIM domain. Google | From: domain aligned with the SPF or the DKIM domain; relaxed is fine. Yahoo | At least one of SPF or DKIM aligned with the From: domain. Microsoft |
| DKIM key length | all senders | 1024 bits or longer; 2048 recommended. Google | 1024 bits or longer; 2048 recommended. Yahoo | Not stated. |
| Reverse DNS (PTR) | all senders | Valid forward and reverse DNS required. Google | Valid forward and reverse DNS required. Yahoo | Required by Outlook.com’s sender policy for every sending server. Microsoft |
| TLS | all senders | Required. Google | Not stated. | Not stated. |
| Spam complaint rate | all senders | Below 0.3%, aim for below 0.1% (Postmaster Tools). Google | Below 0.3%, counted on mail delivered to the inbox. Yahoo | Not stated. |
| One-click unsubscribe | bulk marketing mail | Required (RFC 8058 List-Unsubscribe with an HTTPS URL; mailto alone does not count). Google Google | Required; RFC 8058 POST recommended, mailto accepted. Yahoo Yahoo | No one-click rule stated; Outlook.com’s sender policy requires an unsubscribe that is clearly documented and easy to find. Microsoft |
| Visible unsubscribe link | bulk marketing mail | Required in the message body. Google | Required in the message body. Yahoo | An unsubscribe that is easy to find, under Outlook.com’s sender policy. Microsoft |
| Honour unsubscribes within | bulk senders | 48 hours. Google | 2 days. Yahoo | Not stated. |
| Message format | all senders | RFC 5322. Google | RFC 5321 and RFC 5322. Yahoo | IETF standards; Outlook.com’s policy names RFC 2821 and 2822, since replaced by 5321 and 5322. Microsoft |
| What happens if you miss them | enforcement | Rejection (temporary or permanent) or the spam folder; enforcement stepped up in November 2025. A spam rate over 0.3% or a missing DMARC record also costs delivery support. Google | Spam folder or rejection with an error code. Yahoo | Rejected with 550 5.7.515 Access denied. Microsoft |
| In force since | dates | 1 February 2024; one-click unsubscribe from 1 June 2024. Google Google | February 2024; one-click unsubscribe from June 2024. Yahoo Yahoo | 5 May 2025. Microsoft |
Which mailboxes these rules cover
Gmail’s rules apply to personal accounts ending in @gmail.com or @googlemail.com, not to Google Workspace mailboxes. Yahoo’s apply to every consumer domain Yahoo Mail hosts, AOL included. Microsoft’s apply to Outlook.com and its other consumer domains (Hotmail, Live.com, MSN), and once a domain sends 5,000 messages a day, to every message from that domain. Sources: Google Google Yahoo Microsoft Microsoft.
Where they differ
- One-click unsubscribe: Gmail accepts only an RFC 8058 List-Unsubscribe header with an HTTPS URL; Yahoo also accepts mailto; Outlook.com asks only for an unsubscribe that is easy to find.
- Who is bulk: Gmail draws the line near 5,000 messages a day and Microsoft at 5,000 a day from one From domain; Yahoo publishes no number. Gmail counts all mail from one primary domain together, and a sender that crosses the line once stays bulk.
- Below the line: Gmail and Yahoo still require SPF or DKIM, reverse DNS and a spam rate under 0.3% from every sender; Outlook.com’s SPF, DKIM and DMARC rules apply only to bulk senders, but its sender policy requires valid reverse DNS from every sending server.
Sources
Every cell links the provider page it paraphrases; each rests on a short quote from that page, read 21 Oct 2026 and re-read weekly by a script. “Not stated” means we did not find the requirement on: senders.yahooinc.com senders.yahooinc.com sendersupport.olc.protection.outlook.com substrate.office.com support.microsoft.com. How the data pages are built.