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
I don't know whether it turns on edns0 by default, or whether that has
to be done explicitly in /etc/resolv.conf.
If adding "options edns0" to /etc/resolv.conf does not solve the
problem, another solution may be:
https://dilbert.com/strip/1995-06-24
--
Viktor.
