Looked into the public side of this since it's an interesting case. A few things that might help narrow it down. The basics check out, so this doesn't look like an authentication or rDNS problem:
* .40/.41/.42/.43 all have matching forward and reverse DNS (smtp01-04.cbsolt.net), so FCrDNS is fine. * SPF on both qboxmail.com and qboxmail.it hard fails (-all), and DMARC is p=quarantine with rua reporting on both. * None of the four IPs are listed on Spamhaus ZEN, Barracuda, SpamCop, SORBS, UCEPROTECT level 1, or PSBL. Matches what you're seeing elsewhere. Worth noting: the bounce fires at MAIL FROM, before DATA. That's a connection-level reputation gate, not a per-message content or DKIM verdict. What stood out was the /24 itself. RIPE has 185.97.217.0/24 registered to you as Qboxmail-Email-Hosting-2, but your mailbox relay isn't the only thing in there. A few other PTRs in the same block: 185.97.217.150 -> lvs-delivery01.smtpfy.com 185.97.217.200 -> smtp-dl01-trs01.smtpfy.com 185.97.217.230 -> smtp-dl03-mrk01.smtpfy.com Smtpfy's own site describes it as a Qboxmail product for transactional and marketing sending, with no daily or hourly limit. Your SPF on qboxmail.com/.it also authorizes the whole /22 (185.97.216.0/22) through the spf.qboxmail.com include, so at the DNS level the mailbox relay and the bulk sending platform aren't really separated. If Smtpfy picked up a complaint spike or a trap hit around the 17th, that would explain clean, individually unlisted IPs like .40-.43 getting caught. My read: Yahoo and AOL often escalate from one bad IP to the surrounding range once they attribute a pattern to an operator, which tracks with spammers historically rotating through a block to dodge single-IP blocks. Worth pulling Smtpfy's send volume and complaint/FBL data for the few days before the block, if you haven't already. That would answer this faster than the support form will. Yahoo doesn't publish specifics on TSS09 itself, but the general TS-code family is documented as complaint and reputation driven rather than authentication driven, which lines up with everything above. If the shared /24 turns out to be the cause, the durable fix is separating IP space by traffic type: a dedicated range for the mailbox relay that doesn't overlap the bulk platform, ideally not sharing a /22 either. Domain-level isolation (separate DKIM per sending domain, which Smtpfy already does) doesn't protect IP-level reputation, and Yahoo in particular seems to be acting on the IP/network signal here, not the domain. Two smaller things, unlikely to be the trigger but worth fixing regardless: DKIM on both domains is still a roughly 1024-bit RSA key at selector k1, and DMARC is p=quarantine rather than p=reject on both. On Yahoo support: for a permanent-deferral code like this, they generally want evidence the root cause was found and stopped. A delisting request alone usually won't move it, and even then it can take a while. Sender Hub (senders.yahooinc.com) might move faster than the generic form, if that's not already the channel you're using. You've clearly been through some Yahoo verification before, given the yahoo-verification-key TXT records on qboxmail.it and cbsolt.net. Hope this helps in some way.. ________________________________ From: mailop <[email protected]> on behalf of Alessio Cecchi via mailop <[email protected]> Sent: 21 September 2026 08:21 To: [email protected] <[email protected]> Subject: [mailop] Yahoo has blocked all our IPs Hi, We are Qboxmail, an Italian mailbox hosting provider. We provide only B2B mailboxes exclusively to companies and do not offer free email accounts. I am writing here because I need your help with a deliverability issue affecting Yahoo mailboxes. Starting from September 17th all our SMTPs were blocked by Yahoo: status=bounced (host mx-eu.mail.am0.yahoodns.net[188.125.72.73] said: 553 5.7.2 [TSS09] All messages from 185.97.217.40 will be permanently deferred; Retrying will NOT succeed. See https://postmaster.yahooinc.com/error-codes (in reply to MAIL FROM command)) dsn=5.7.2, status=bounced (host mta7.am0.yahoodns.net[67.195.204.74] said: 553 5.7.2 [TSS09] All messages from 185.97.217.41 will be permanently deferred; Retrying will NOT succeed. See https://postmaster.yahooinc.com/error-codes (in reply to MAIL FROM command)) dsn=5.7.2, status=bounced (host mta6.am0.yahoodns.net[98.136.96.74] said: 553 5.7.2 [TSS09] All messages from 185.97.217.43 will be permanently deferred; Retrying will NOT succeed. See https://postmaster.yahooinc.com/error-codes (in reply to MAIL FROM command)) All our IPs 185.97.217.0/24 seems blocked by Yahoo. I filled out the support form on their website, but nothing has changed. It’s very strange because we’re only having this problem with Yahoo; our IPs aren't on any other major blocklists. We’re facing serious issues because of this block. What can we do? Thanks -- Alessio Cecchi postmaster AT qboxmail https://it.linkedin.com/in/alessice _______________________________________________ mailop mailing list [email protected] https://list.mailop.org/listinfo/mailop
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