# Bulk Sender Requirements Checker URL: https://iblockspam.com/tools/bulk-sender-checker Last updated: 2026-10-10 > Enter the domain you send from to see which Gmail, Yahoo and Outlook.com sender requirements it meets in DNS, and what you still need to check in your email platform. Free tool: Check your domain against the Gmail, Yahoo and Outlook.com bulk sender rules that DNS can show, with a checklist per provider. Use it at https://iblockspam.com/tools/bulk-sender-checker ## What the Bulk Sender Requirements Checker does It reads your domain's public DNS and maps what it finds onto the written rules of the three largest consumer mailbox providers: [Gmail](https://support.google.com/mail/answer/81126), [Yahoo](https://senders.yahooinc.com/best-practices/) and [Outlook.com](https://support.microsoft.com/en-us/Outlook/fix-ndr-error-550-5-7-515-in-outlook-com). You get a checklist per provider, an overall verdict, and a fix for each problem. Gmail treats anyone sending close to 5,000 or more messages a day to personal Gmail accounts as a bulk sender. Outlook.com applies its rules above 5,000 messages a day to its consumer addresses. Yahoo doesn't publish a number. Some rules, such as reverse DNS at Gmail and Yahoo, apply to every sender, whatever the volume. ## What we can check from DNS - **SPF.** One valid record, within the limit of 10 DNS lookups, that authorizes at least one sender. Over the limit, receivers return a permanent error and SPF stops counting. Build a record with the [SPF Record Generator](https://iblockspam.com/tools/spf-generator). - **DKIM.** A valid public key at the selector you enter, or at one of eight common selectors. Gmail requires keys of at least 1024 bits. Create a key pair with the [DKIM Key Generator](https://iblockspam.com/tools/dkim-generator). - **DMARC.** A single record with a valid policy. All three providers accept `p=none` as the minimum. Write one with the [DMARC Record Generator](https://iblockspam.com/tools/dmarc-generator). - **Reverse DNS.** If you enter a sending IP, we check its PTR record and that the name resolves back to the same address (forward-confirmed reverse DNS). Gmail and Yahoo require this for every sender. - **MX or A record.** A domain that can't receive mail can't get replies or bounces. Microsoft recommends a From or Reply-To address that can receive replies. ## What DNS can't show These requirements are real, but they live in your messages or in the providers' data. The checker marks them "Check manually" and never as passed: - **Alignment.** Your From: domain must align with the domain that passes SPF or DKIM. DNS shows that you publish records, not which domain your platform actually signs with. Send a message to the free [Email Deliverability Test](https://iblockspam.com/tools/deliverability-test) and look for `dmarc=pass`. - **TLS.** Gmail requires a TLS connection. That's negotiated per connection, and the deliverability test reports it for one real message. - **One-click unsubscribe.** Gmail and Yahoo require `List-Unsubscribe` and `List-Unsubscribe-Post` headers on marketing mail. See [one-click unsubscribe (RFC 8058)](https://iblockspam.com/blog/one-click-unsubscribe-rfc-8058). - **Spam complaint rate.** Gmail and Yahoo set 0.3% as the limit, and Google recommends staying under 0.1%. Only the providers can measure it: see [spam complaint rates explained](https://iblockspam.com/blog/spam-complaint-rate-explained), the [Google Postmaster Tools guide](https://iblockspam.com/blog/google-postmaster-tools-guide) and [Outlook.com SNDS and JMRP](https://iblockspam.com/blog/outlook-com-deliverability-snds-jmrp). - **Message format.** Gmail requires RFC 5322 formatting and a single address in From:. Yahoo requires RFC 5321 and RFC 5322. ## How to read the results - **Meets the DNS-checkable requirements.** Everything DNS can show is in place. Confirm the manual items before you call the job done. - **Incomplete.** Nothing failed, but something couldn't be confirmed: usually a DKIM selector we couldn't find, or a lookup that timed out. - **Doesn't meet.** At least one record is missing or broken. Fix those first, because receivers check them on every message. Outlook.com rejects mail from high-volume domains that fail its requirements with [550 5.7.515](https://iblockspam.com/smtp-errors/550-5-7-515). Gmail's authentication rejection is [550 5.7.26](https://iblockspam.com/smtp-errors/550-5-7-26). ## Limitations - We check the domain you enter. If your platform sends with a different envelope (return-path) domain, check that domain's SPF too. - Microsoft says SPF and DKIM must both *pass*. We can only see that the records are published and valid; whether they pass depends on which servers send and how they sign. - Each provider's rules change over time. We last checked the sources below on October 10, 2026. The full comparison is in our guide to [Gmail, Yahoo and Microsoft bulk sender requirements](https://iblockspam.com/blog/gmail-yahoo-microsoft-bulk-sender-requirements). ## Sources - Google, Gmail Help: [Email sender guidelines](https://support.google.com/mail/answer/81126) and [Email sender guidelines FAQ](https://support.google.com/mail/answer/14229414) - Yahoo Sender Hub: [Sender best practices](https://senders.yahooinc.com/best-practices/) - Microsoft Community Hub: [Strengthening Email Ecosystem: Outlook's New Requirements for High-Volume Senders](https://techcommunity.microsoft.com/blog/microsoftdefenderforoffice365blog/strengthening-email-ecosystem-outlook%E2%80%99s-new-requirements-for-high%E2%80%90volume-senders/4399730) - Microsoft Support: [Fix NDR error 550 5.7.515 in Outlook.com](https://support.microsoft.com/en-us/Outlook/fix-ndr-error-550-5-7-515-in-outlook-com) - IETF: [RFC 8058, one-click unsubscribe](https://www.rfc-editor.org/rfc/rfc8058.html) and [RFC 7208, SPF](https://www.rfc-editor.org/rfc/rfc7208.html) ## Frequently asked questions ### Does passing this check mean my domain is compliant with Gmail and Yahoo rules? No. It means your domain meets the requirements that public DNS can show: SPF, DKIM, DMARC, reverse DNS for an IP you enter, and a working MX. TLS, alignment of your real messages, one-click unsubscribe and your spam rate can only be confirmed from your messages and the providers' own dashboards. ### Why does the checker say my DKIM is unknown? DKIM keys are published under a selector name, and DNS has no way to list them. We try eight common selectors. If yours has a different name, enter it in the selector box. You can find it in the s= tag of the DKIM-Signature header of a message you sent. ### Which IP address should I enter as the sending IP? The public IP address of the server that hands your mail to Gmail, Yahoo or Outlook.com. It appears in the Received header that the receiving provider adds, near the top of the headers. If you send through Google Workspace, Microsoft 365 or an email service provider, they manage reverse DNS for their own IPs, so you can leave the box empty. ### Do the bulk sender rules apply to Microsoft 365 business mailboxes? Microsoft's published high-volume sender requirements cover Outlook.com, its consumer service, including hotmail.com and live.com addresses. Mail to Microsoft 365 business mailboxes is filtered too, but under each organization's own policies rather than this published threshold. --- Source: iBlockSpam, https://iblockspam.com/tools/bulk-sender-checker (this is a Markdown copy; the HTML page is canonical). Quote with attribution and a link. Site index for AI assistants: https://iblockspam.com/llms.txt