In my experience, "Sender address rejected: Domain not found", when you expect the sender's domain to be legitimate, can mean that the sender is having a DNS configuration issue or didn't renew their domain registration.
But in this case, because thesparklebar.com is a legitimate domain whose MX record points to Google, I would suspect that some marketer at thesparklebar.com learned that from all of the email deliverability best practices guides that you should send marketing emails from a subdomain, like zf.thesparklebar.com. Those guides too often presume that IT will be involved in configuring the needed (and correct) email-related DNS records and getting them in place _before_ one starts sending email from the subdomain. So let's check: root@bind4:~# dig zf.thesparklebar.com TXT +short "v=spf1 a:opzcxi.thesparklebar.com -all" root@bind4:~# host opzcxi.thesparklebar.com opzcxi.thesparklebar.com has address 88.198.143.50 root@bind4:~# host 88.198.143.50 50.143.198.88.in-addr.arpa domain name pointer static.88-198-143-50.clients.your-server.de. root@bind4:~# You won't be the only one rejecting such emails. The sender will likely figure it out soon enough. Hope that helps, Mark -- _________________________________________________________________ L. Mark Stone, Founder North America's Leading Zimbra VAR/BSP/Training Partner For Companies With Mission-Critical Email Needs Winner of the Zimbra Americas VAR Partner of the Year - Two Years Running ! ----- Original Message ----- | From: "Chris via mailop" <[email protected]> | To: "Ralph Mayer" <[email protected]> | Cc: [email protected] | Sent: Thursday, November 13, 2025 6:39:58 PM | Subject: Re: [mailop] Google trying to send mail to nonexistent users - going for about a month | On 2025-11-13 13:28, Ralph Mayer via mailop wrote: |> Dear mailops, |> |> I need some ideas how to deal with this (small snippet from my logs) |> |> Nov 13 22:10:51 bert postfix/smtpd[2693931]: NOQUEUE: reject: RCPT from |> mail-oi1-x248.google.com[2607:f8b0:4864:20::248]: 450 4.1.8 |> <[email protected]>: Sender address |> rejected: Domain not found; |> from=<[email protected]> |> to=<[email protected]> proto=ESMTP helo=<mail-oi1-x248.google.com> |> Nov 13 22:12:07 bert postfix/smtpd[2696594]: NOQUEUE: reject: RCPT from |> mail-ua1-x948.google.com[2607:f8b0:4864:20::948]: 450 4.1.8 |> <[email protected]>: Sender address |> rejected: Domain not found; |> from=<[email protected]> |> to=<[email protected]> proto=ESMTP helo=<mail-ua1-x948.google.com> |> Nov 13 22:12:18 bert postfix/smtpd[2696594]: NOQUEUE: reject: RCPT from |> mail-wm1-x346.google.com[2a00:1450:4864:20::346]: 450 4.1.8 |> <[email protected]>: Sender address |> rejected: Domain not found; |> from=<[email protected]> |> to=<[email protected]> proto=ESMTP helo=<mail-wm1-x346.google.com> |> Nov 13 22:12:37 bert postfix/smtpd[2696594]: NOQUEUE: reject: RCPT from |> mail-lf1-x146.google.com[2a00:1450:4864:20::146]: 450 4.1.8 |> <[email protected]>: Sender address |> rejected: Domain not found; |> from=<[email protected]> |> to=<[email protected]> proto=ESMTP helo=<mail-lf1-x146.google.com> |> Nov 13 22:13:08 bert postfix/smtpd[2696594]: NOQUEUE: reject: RCPT from |> mail-lj1-x248.google.com[2a00:1450:4864:20::248]: 450 4.1.8 |> <[email protected]>: Sender address |> rejected: Domain not found; |> from=<[email protected]> |> to=<[email protected]> proto=ESMTP helo=<mail-lj1-x248.google.com> |> Nov 13 22:13:08 bert postfix/smtpd[2696594]: NOQUEUE: reject: RCPT from |> mail-wm1-x345.google.com[2a00:1450:4864:20::345]: 450 4.1.8 |> <[email protected]>: Sender address |> rejected: Domain not found; |> from=<[email protected]> |> to=<[email protected]> proto=ESMTP |> helo=<mail-wm1-x345.google.com> |> Nov 13 22:14:03 bert postfix/smtpd[2696594]: NOQUEUE: reject: RCPT from |> mail-lj1-x248.google.com[2a00:1450:4864:20::248]: 450 4.1.8 |> <[email protected]>: Sender address |> rejected: Domain not found; |> from=<[email protected]> |> to=<[email protected]> proto=ESMTP helo=<mail-lj1-x248.google.com> |> |> As you can see, the to-address is generated and its different hosts at |> google |> trying to send mails. |> |> Searching for zf.thesparklebar.com <http://zf.thesparklebar.com/> shows |> others |> having the same problem. |> |> [email protected] <mailto:[email protected]> did not respond |> |> Also, why does this not trigger countermeasures at Google? | This smells like transient DNS failures. IOW no IP address could be found for | host(name). | |> |> |> Best regards |> Ralph |> _______________________________________________ |> mailop mailing list |> [email protected] |> https://list.mailop.org/listinfo/mailop | | _______________________________________________ | mailop mailing list | [email protected] | https://list.mailop.org/listinfo/mailop _______________________________________________ mailop mailing list [email protected] https://list.mailop.org/listinfo/mailop
