MSGID: <10fi386$1km85$4@dont-email.me> 046d131e
REPLY:  390381d4
PID: PyGate 1.5
TID: PyGate/Linux 1.5
CHRS: ASCII 1
TZUTC: 0000
REPLYADDR tnp@invalid.invalid
REPLYTO 3:633/10 UUCP
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


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