Steffen Nurpmeso wrote in
<20250102200053.OMpeoSDb@steffen%sdaoden.eu>:
|Wietse Venema via Postfix-users wrote in
| <4ypcfw1rmdzj...@spike.porcupine.org>:
||Joachim Lindenberg:
| ...
||Joachim Lindenberg:
||> To some extend the approach probably replaces blocking calls on
||> TCP layer with blocking calls on DNS. If we see DNS also moving
||
||Postfix blocks on DNS. The SMTP reads and writes are also blocking.
||The TLS reads and writes are non-blocking if implemented in tlsproxy,
||and blocking if implemented in the SMTP client itself.
|
|Only to note that RRs can be and usually are cached. (I use
...
| # dig _imaps._tcp.gmail.com SRV
| ...
| _imaps._tcp.gmail.com. 21600 IN SRV 5 0 993 imap.gmail.com.
|
|Six hours.
|
| # dig _smtps._tcp.sdaoden.eu SRV
| ...
| _smtps._tcp.sdaoden.eu. 14400 IN SRV 0 1 26 sdaoden.eu.
|
|Four hours. (I do not control that, i have only a web form.)
...
For the full truth it must be added that negative caching (RFC
2308) is usually far less extensive, i have
* The maximum value is 300 seconds (five minutes, RFC 2308, 7.1.).
So that likely is it. Usually user configurable in addition.
I do not know what postfix does.
Yes, that is not nice. Super-small UDP. But not nice.
(I will not add a comparison to what other things do, ie, opening
a "modern" web page, or what. But one thing: *if* the SRV record
exists, the MX will not be tried, and the TCP based SMTP
roundtrips are worlds more expensive; having said that, the
"this service does not exist here" SRV possibility, as in
# dig _imap._tcp.gmail.com SRV
...
_imap._tcp.gmail.com. 79629 IN SRV 0 0 0 .
should possibly be mentioned in the draft. This could end up with
a TTL of a whole day, it seems.)
--steffen
|
|Der Kragenbaer, The moon bear,
|der holt sich munter he cheerfully and one by one
|einen nach dem anderen runter wa.ks himself off
|(By Robert Gernhardt)
|
|In Fall and Winter, feel "The Dropbear Bard"s pint(er).
|
|The banded bear
|without a care,
|Banged on himself for e'er and e'er
|
|Farewell, dear collar bear
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