**Steps to replicate the issue** (include links if applicable):
* Try to reply to an @yahoo.com customer in VRT
* FAIL: Get error message
**What happens?**:
Error bounce back:
Reporting-MTA: dns; mx-out1001.wikimedia.org
X-Postfix-Queue-ID: 4gBJCG3fYxzMssd
X-Postfix-Sender: rfc822; vrts-bounce@wikimedia.org
Arrival-Date: Thu, 7 May 2026 16:50:18 +0000 (UTC)
Final-Recipient: rfc822; REDACTED@yahoo.com
Original-Recipient: rfc822;REDACTED@yahoo.com
Action: failed
Status: 4.7.0
Remote-MTA: dns; mta7.am0.yahoodns.net
Diagnostic-Code: smtp; 421 4.7.0 [TSS04] Messages from 208.80.154.5 temporarily
deferred due to unexpected volume or user complaints - 4.16.55.1; see
https://postmaster.yahooinc.com/error-codes
**What should have happened instead?**:
Mail should have gone through
**Software version** (on `Special:Version` page; skip for WMF-hosted wikis like Wikipedia):
WMF Production
**Other information** (browser name/version, screenshots, etc.):
This is technically a THEM problem, but it affects US