Subj : Re: ODD DNS behaviour on Pi ZERO W with Bullseye OS To : All From : The Natural Philosopher Date : Tue Nov 18 2025 15:27:01 On 18/11/2025 14:37, Theo wrote: > The Natural Philosopher wrote: >> As part of my enhancements to the home controller, I want to send email >> warnings of low heating oil level. >> >> So I removed exim which was too much like hard work, installed PostFix >> and all is well...,except it isn't. >> >> If I send a mail out of the blue after a a few hours delay, the mail >> immediately *always* gets stuck in the queue with a message about being >> unable to determine the IP address of the SMTP relay. >> >> If I send another message everything Just Works, and indeed the h mail >> queue gets flushed eventually as well with a successful delivery. > > 'Greylisting'? SMTP servers often delay mail from unrecognised senders as a > spam block - spammers tend not come back when told to try again later. > Its my smtp server. Sorry I didn't make that clear. No greylisting that I am aware of > Also the message needs to be correct to match SFP/DKIM/DMARC rules, > otherwise it may get delayed or discarded. It may also be delayed/discarded > due to sending from a 'consumer' IP. > Again, there is no issue as its set to accept any mail from anywhere that is addressed to my home network. > Perhaps by the time the second message arrives the spamfilter has decided > you're ok and to let the message straight through. > 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) Nov 18 10:56:42 heating-controller postfix/qmgr[1295]: CC05B1F270: from=, size=387, nrcpt=1 (queue active) Nov 18 10:56:43 heating-controller postfix/smtp[10697]: CC05B1F270: to=, relay=vps.templar.co.uk[185.113.128.151]:25, delay=587, delays=586/0.22/0.64/0.08, dsn=2.0.0, status=sent (250 OK id=1vLJO7-0000r9-GS) Nov 18 10:56:43 heating-controller postfix/qmgr[1295]: CC05B1F270: removed > I would not be doing direct SMTP in this day and age - send using an SMTP > account (with username/password) at the company who runs the SMTP server for > the sender's mail domain. > Sigh. I do for mail outward bound, but this is actually inward boiund. > If the SMTP relay is indeed your domain's mail server, perhaps the first > time DNS lookup is too slow? > Its something like that. Let me say that all other boxes inside the network that are equipped for mail work fine > Theo -- For every complex problem there is an answer that is clear, simple, and wrong. H.L.Mencken --- PyGate Linux v1.5 * Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10) .