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Guides

Provider blocks

What happens when one mailbox provider refuses or throttles your mail, what the platform does about it, and where to delist.

Your mail to one mailbox provider stopped, while mail to every other provider still arrives. This is a provider block. This guide explains what the platform does and what you do.

What a provider block is

A provider block is a reputation or policy reply from the receiving provider. The provider refuses the message (a bounce) or asks the platform to retry later (a delay). The reply text names the cause: a listed sending address, an unusual volume, too many complaints, or content the provider rejects. The block applies to that provider only.

What the platform does

  • On every bounce or delay, the platform classifies the reply of the provider. It stores the classification on the event, so the message timeline shows it.

  • The Metrics page counts the classified replies as Blocked per provider. A block at one provider shows there before it moves the totals.

  • A Provider block alert rule with Pause sending on opens a hold on that provider. The hold lasts 4 hours by default. Mail to that provider waits in the queue. Mail to every other provider keeps flowing. The organization stays active.

  • The platform sends an e-mail to every admin of the organization. The e-mail and the banner in the console show the code, the provider and the delist link.

  • The audit log records the hold and the release.

  • A released hold opens again only on a new block.

The delivery provider owns the sending addresses, so the Refresh team also files a delist where the provider has a form. Your own request, with the reply text of your message, speeds the review. The table below tells you where to file.

Codes

The platform recognises these replies. Hold means a Provider block rule with Pause sending can open a hold. Observe means the platform counts and shows the reply but never holds mail for it.

Code Provider What the reply means What the platform does Where to delist
MS_S3140 Microsoft Microsoft S3140 network block Hold https://sender.office.com/ or delist@microsoft.com. Include the full SMTP reply text and the blocked IP. Use the delist portal; if the NDR is 5.7.511, forward the NDR to delist@microsoft.com.
MS_S3150 Microsoft Microsoft S3150 network block Hold Same as MS_S3140.
MS_5_7_511 Microsoft Microsoft 5.7.511 banned sender Hold Same as MS_S3140; forward the NDR to delist@microsoft.com.
MS_4_7_650 Microsoft Microsoft 4.7.650–699 IP reputation throttle Hold Same as MS_S3140.
MS_5_7_1_SPAMHAUS Microsoft Microsoft 5.7.1 Spamhaus block Hold Same as MS_S3140. Also check https://check.spamhaus.org/ for the listing.
GMAIL_421_4_7_0 Gmail Gmail 421 4.7.0 unusual rate / IP reputation Hold https://support.google.com/mail/contact/bulk_send_new. Check Google Postmaster Tools first, then file a bulk-sender appeal with the SMTP reply and sending IP.
GMAIL_421_4_7_28 Gmail Gmail 4.7.28 unusual rate Hold Same as GMAIL_421_4_7_0.
GMAIL_550_5_7_1 Gmail Gmail 550 5.7.1 content / policy Observe Same as GMAIL_421_4_7_0. The cause is usually the content or the links; fix those first.
YAHOO_TSS04 Yahoo Yahoo TSS04 volume / complaint throttle Hold https://senders.yahooinc.com/contact/. Submit a sender support request with the SMTP reply and sending IP.
YAHOO_TSS09 Yahoo Yahoo TSS09 permanent deferral Hold Same as YAHOO_TSS04.
DNSBL_SPAMCOP Any (SpamCop listing) SpamCop DNSBL Hold https://www.spamcop.net/bl.shtml. Look up the listed IP. SpamCop listings expire automatically; request removal if still listed.
DNSBL_SPAMHAUS Any (Spamhaus listing) Spamhaus DNSBL Hold https://check.spamhaus.org/. Look up the listed IP or domain and follow the SBL/XBL/ZEN delist instructions.

A DNSBL row applies to whichever provider quoted the list in its reply. The hold then covers that provider.

What you do

  1. Open the message in Emails and read the reply next to the bounce or delay on the timeline.
  2. Find the code in the table above and delist where the table says. Attach the full reply text.
  3. Check the Blocked column on Metrics for that provider over the next hours.
  4. Release the hold from the banner when the provider confirms, or let the hold expire.
  5. If the block returns, lower the volume to that provider and review the complaints of the last days.

If a listing continues for more than a day after you filed, write to support with the reply text.