David Dolan:
> On Fri, 2 Dec 2022 at 10:33, David Dolan <daithido...@gmail.com> wrote:
>
> >
> >
> > 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
> >
> This is from the mail relay which says it's truncated and trying tcp mode.
> It does return all 33 IP addresses
> dig wx-use2.prod.hydra.sophos.com
> ;; Warning: Message parser reports malformed message packet.
> ;; Truncated, retrying in TCP mode.
>
> I guess it's using the musl resolver in Alpine so we need to migrate OS to
> get past this issue?
Yes. Don't use toy software in production.
Wietse
