Our customers who use yahoo.com e-mail addresses are saying they aren't receiving invoices from our billing system. I checked our mail logs and I'm getting this: Jan 12 16:11:34 account postfix/smtp[9802]: 1FA906C0E61: host mta7.am0.yahoodns.net[98.136.101.117] said: 421 4.7.0 [TSS04] Messages temporarily deferred due to user complaints - 4.16.55.1; see https://help.yahoo.com/kb/postmaster/SLN3434.html (in reply to MAIL FROM command) The link suggests several things to do and we've waited over 48 hours and still can't get invoices through. The invoice server is definitely not compromised, and honestly I can't imagine there would be enough complaints to trigger a global block of that IP address, and we only have a small number of customers using @epix.net e-mail addresses. Thanks!