Mailing list subscription's mail delivery delays?

Hi,

By lack of a better place to ask:

I've recently noticed that in several of the email threads that I
follow over on -hackers@ that some of the email messages have a very
high time-to-delivery, and thus mails from the same thread arrive
out-of-order.
I've seen several occurances of this with very long delays of over 10
hours, with at least one larger than 19 hours, assuming mail server
clocks are accurate and receipt dates are correctly included in the
mail headers.

I'm not sure if the issue is on my side (mail servers are gmail's) or
on the mailing list server - all traces I've checked indicate that the
delay is somewhere in the delivery from postgres' last mail server to
the first gmail mail server.

I've only really noticed this sometime in the past few weeks. After
sampling my mails, I found other examples of significant delays (>1h)
for mails from well-respected hackers dating back to at least
2023-08-28.

Would you happen to know why this could be the case, and what I can do
to fix it if it's something on my side?

I've attached three recently received mails from -hackers as .eml, to
help with any debugging: one was delivered relatively quickly (91s),
one for which the delivery took a long time (11h+) and one more with a
very long delivery time (19h+). I haven't yet noticed any specific
differences or commonalities between fast and slow mails.

Kind regards,

Matthias van de Meent.