Who counts as a bulk sender
Google and Microsoft both draw the line at 5,000 messages a day. Send 5,000 or more a day to Gmail accounts and Google counts you as a bulk sender. Send as many to Outlook.com, Hotmail and Live and Microsoft's rules apply to you. The count is of mail to that provider's own addresses, not of everything you send. Yahoo also sets rules for bulk senders, but its page gives no number.
Below the line, Gmail and Yahoo still require SPF or DKIM from every sender.
Sources: Google, email sender guidelines; Microsoft, error 550 5.7.515; Yahoo, sender best practices.
What each provider requires
| Provider | Since | What it requires |
|---|---|---|
| Gmail | 1 February 2024 | SPF or DKIM from every sender. SPF, DKIM and a DMARC record from anyone sending 5,000 or more messages a day. |
| Yahoo | February 2024 | SPF and DKIM from bulk senders, and a DMARC policy of at least none that passes. |
| Microsoft | 5 May 2025 | SPF, DKIM and DMARC from senders of 5,000 or more messages a day to Outlook.com, Hotmail and Live. Mail that fails is rejected with error 550 5.7.515. |
Source: Microsoft, Outlook's new requirements for high-volume senders.
What happens to mail that fails
Microsoft rejects it, and the sender gets a bounce that reads: 550 5.7.515 Access denied, sending domain <domain> does not meet the required authentication level. Gmail may mark it as spam or reject it. Yahoo warns that its delivery will suffer.
Sources: Microsoft, error 550 5.7.515; Google, email sender guidelines; Yahoo, sender best practices.
What the rules do not require
None of the three requires enforcement. They require a DMARC record from bulk senders, and p=none meets that. The rules are why your mail needs the records. Enforcement is what protects you.
One-click unsubscribe and complaint rates
Google requires bulk senders to let people unsubscribe from marketing and subscribed messages in one click: each message carries a List-Unsubscribe header and the header List-Unsubscribe-Post: List-Unsubscribe=One-Click. Yahoo asks for a functioning list-unsubscribe header that supports one-click unsubscribe for marketing and subscribed messages, and for unsubscribes to be honoured within two days.
Sources: Google, email sender guidelines; Yahoo, sender best practices.
A complaint rate is the share of your mail that people report as spam, which Google and Yahoo call the spam rate. Google requires every sender to keep the spam rate reported in Postmaster Tools below 0.3%, and asks for it to stay below 0.10% and never to reach 0.30% or higher. Yahoo asks senders to keep their spam rate below 0.3%.
Sources: Google, email sender guidelines; Yahoo, sender best practices.
A checklist
- SPF passes
- DKIM signs with your own domain
- A DMARC record exists
- The From domain aligns with the SPF or the DKIM domain
- Reverse DNS is valid
Sources: Google, email sender guidelines; Yahoo, sender best practices; Microsoft, error 550 5.7.515.
How to check yours
The free check reads your SPF, DKIM and DMARC records and your mail servers' reverse DNS in about 30 seconds, and says in plain English what they mean. It reads only what is already public, so it cannot see your mail itself: your spam rate at Gmail is in Google's Postmaster Tools, and whether each of your senders passes shows in your DMARC reports.