From: invalid@invalid.invalid   
      
   The Natural Philosopher  writes:   
   > On 18/11/2025 21:08, Computer Nerd Kev wrote:   
   >> The Natural Philosopher  wrote:   
   >>> Seriously,m its not the server, its the DNS.   
      
   >>> It (the PI) cant even *find* the SMTP server   
   >>> Nov 18 10:46:56 heating-controller postfix/pickup[8654]: CC05B1F270:   
   >>> uid=0 from=   
   >>> Nov 18 10:46:56 heating-controller postfix/cleanup[10455]: CC05B1F270:   
   >>> message-id=<20251118104656.CC05B1F270@heating-controller>   
   >>> Nov 18 10:46:56 heating-controller postfix/qmgr[1295]: CC05B1F270:   
   >>> from=, size=387, nrcpt=1 (queue active)   
   >>> Nov 18 10:46:57 heating-controller postfix/smtp[10457]: CC05B1F270:   
   >>> to=, relay=none, delay=0.38,   
   >>> delays=0.19/0.14/0.04/0, dsn=4.4.3, status=deferred (Host or domain name   
   >>> not found. Name service error for name=vps.templar.co.uk type=MX: Host   
   >>> not found, try again)   
   >>   
   >> If it's the only network activity the thing does regularly, maybe   
   >> the WiFi interface has gone into some sort of sleep mode and the DNS   
   >> resolver isn't waiting for it to wake up. If you leave ping running   
   >> (eg. "nohup ping -s 1 vps.templar.co.uk &") to keep the interface   
   >> active, maybe it will work the first time?   
   >>   
   > I was logged in over ssh at the time, so that hound don't hunt :-(   
      
   Was the SSH session actually doing anything? An idle SSH session doesn’t   
   have to exchange any packets at all.   
      
   But “it’s always DNS” is a pretty reliable starting point for network   
   debugging, and I think it’s the right one here.   
      
   What are you using as a name server? i.e. what is in resolv.conf on this   
   machine?   
      
   Nov 18 10:46:57 heating-controller postfix/smtp[10457]: CC05B1F270:   
   to=, relay=none, delay=0.38,   
   delays=0.19/0.14/0.04/0, dsn=4.4.3, status=deferred (Host or domain   
   name not found. Name service error for name=vps.templar.co.uk type=MX:   
   Host not found, try again)   
   ^^^^^^^^^^^^^^^^^^^^^^^^^   
      
   It’s a temporary failure, ‘TRY_AGAIN’ ultimately from something in   
   resolv.h or netdb.h, but with a lot of Postfix-specific DNS code around   
   it.   
      
   vps.templar.co.uk.      3600    IN      MX      5 vps.templar.co.uk.   
      
   Your MX record has 1-hour TTL, so an hour after the last successful   
   query, your local (or ISP-provided) name server will have to ask   
   domaincontrol.com again. That may explain why ‘a few hours delay’ brings   
   the condition back.   
      
   domaincontrol.com seems to be pretty fast from here but if for whatever   
   reason the network between you and domaincontrol is slow or unreliable,   
   or the name server you’re using is underprovisioned, then that could   
   explain the temporary failures here. By the time you send the another   
   message everything has caught up, explaining why it works on the second   
   attempt.   
      
   --   
   https://www.greenend.org.uk/rjk/   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)