Subject: Re: helo command rejected > From: Viktor Dukhovni <postfix-users () dukhovni ! org> > Date: 2022-12-01 16:56:13 > Message-ID: Y4jcrRxsEJPsWZVZ () straasha ! imrryr ! org > [Download RAW message or body] > > On Thu, Dec 01, 2022 at 04:06:30PM +0000, David Dolan wrote: > > > This is the full line: > > > > NOQUEUE: reject: RCPT from unknown[103.246.251.109]: > > 450 4.7.1 <wx-use2.prod.hydra.sophos.com>: > > Helo command rejected: Host not found; > > from=<#############> to=<#############> > > proto=ESMTP helo=<wx-use2.prod.hydra.sophos.com> > > Indeed the hostname "wx-use2.prod.hydra.sophos.com" exists and has > multiple IP addresses, requiring support for either TCP or EDNS with a > UDP buffer larger than 512 bytes Perhaps your DNS resolver or the C > library stub resolver are configured to limit DNS to 512 bytes of UDP > and also don't retry over TCP? In that case you'd get only a truncated > response with no answers, and have no way to recover: > > $ dig +nocmd +ignore +norecur +noedns -t a > wx-use2.prod.hydra.sophos.com @ns-1793.awsdns-32.co.uk > ;; Got answer: > ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 14328 > ;; flags: qr aa tc; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0 > > ;; QUESTION SECTION: > ;wx-use2.prod.hydra.sophos.com. IN A > > ;; Query time: 9 msec > ;; SERVER: 205.251.199.1#53(ns-1793.awsdns-32.co.uk) (UDP) > ;; WHEN: Thu Dec 01 11:47:53 EST 2022 > ;; MSG SIZE rcvd: 47 > > Are you on a MUSL libc system? IIRC there's no support for TCP in > MUSL's stub resolver. See, for example: > > https://news.ycombinator.com/item?id=28312935 > We do use Alpine Linux so maybe truncation is the issue? I thought it may have been initially but couldn't find anything confirming
> > I don't know whether it turns on edns0 by default, or whether that has > to be done explicitly in /etc/resolv.conf. > This suggests that Alpine Linux doesn't support tcp or edns0 for dns queries so we may be stuck https://christoph.luppri.ch/fixing-dns-resolution-for-ruby-on-alpine-linux > > If adding "options edns0" to /etc/resolv.conf does not solve the > problem, another solution may be: > > https://dilbert.com/strip/1995-06-24 > >
