Hi, On Tue, Apr 25, 2023 at 1:03 PM Gerald Galster via Postfix-users < postfix-users@postfix.org> wrote:
> Hi, I realize this is probably one of the most frequently asked questions, > but I really can't figure out why this was rejected. > > Apr 25 12:06:01 petra postfix-226/smtpd[592344]: NOQUEUE: reject: RCPT > from mail.email.eurobank.rs[195.242.76.237]: 450 4.1.8 < > u...@eurobank-direktna.rs>: Sender address rejected: Domain not found; > from=<obaveste...@eurobank-direktna.rs> to=<mi...@example.com> > proto=ESMTP helo=<mail.email.eurobank-direktna.rs> > > What am I missing? eurobank-direktna.rs and > mail.email.eurobank-direktna.rs both have forward and reverse DNS entries. > > I thought maybe it just didn't resolve properly at the time the email was > received, but it's been happening for hours. > > > Negative dns answers may be cached but usually not for hours. > Verify that the resolver running on the postfix server can > resolve that domain because this sounds like a dns problem. > > https://www.postfix.org/postconf.5.html#reject_unknown_sender_domain > > Query the resolvers listed in /etc/resolv.conf directly, e.g. > > dig @127.0.0.1 eurobank-direktna.rs a > dig @127.0.0.1 eurobank-direktna.rs mx > That was the problem, thanks. I think it may be due to a low memory issue on the mail server. Simply restarting bind fixed it, but it is definitely curious to me that it was responding properly for so long. Thanks for taking the time to help. > >
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