mailman smtp.log: 

Jan 09 12:00:57 2021 (1571668) Peer: ('127.0.0.1', 51752)
Jan 09 12:00:57 2021 (1571668) ('127.0.0.1', 51752) handling connection
Jan 09 12:00:57 2021 (1571668) ('127.0.0.1', 51752) Data: b'LHLO ****'
Jan 09 12:00:57 2021 (1571668) ('127.0.0.1', 51752) Data: b'MAIL FROM:<****@****>'
Jan 09 12:00:57 2021 (1571668) ('127.0.0.1', 51752) sender: *****@*****
Jan 09 12:00:57 2021 (1571668) ('127.0.0.1', 51752) Data: b'RCPT TO:<*****@*****>'
Jan 09 12:00:57 2021 (1571668) ('127.0.0.1', 51752) recip: ******@********
Jan 09 12:00:57 2021 (1571668) ('127.0.0.1', 51752) Data: b'DATA'
Jan 09 12:00:57 2021 (1571668) ('127.0.0.1', 51752) Data: b'QUIT'
Jan 09 12:00:57 2021 (1571668) ('127.0.0.1', 51752) connection lost
...

Message has been archived properly, mailmansuite.log
INFO 2021-01-09 12:01:00,277 1164814 hyperkitty.views.mailman Archived message <91B190F7-EEA3-4FA7-9808-2C35774E665A@gmail.com> to ***

From mailman error.log
Jan 09 12:01:00 2021 (1571670) Cannot connect to SMTP server 127.0.0.1 on port 25


Jan 09 12:00:58 2021 (1571671) <91B190F7-EEA3-4FA7-9808-2C35774E665A@gmail.com> pipeline default-posting-pipeline processing: validate-authenticity
Jan 09 12:00:58 2021 (1571671) <91B190F7-EEA3-4FA7-9808-2C35774E665A@gmail.com> pipeline default-posting-pipeline processing: mime-delete
Jan 09 12:00:58 2021 (1571671) <91B190F7-EEA3-4FA7-9808-2C35774E665A@gmail.com> pipeline default-posting-pipeline processing: tagger
Jan 09 12:00:58 2021 (1571671) <91B190F7-EEA3-4FA7-9808-2C35774E665A@gmail.com> pipeline default-posting-pipeline processing: member-recipients
Jan 09 12:00:58 2021 (1571671) <91B190F7-EEA3-4FA7-9808-2C35774E665A@gmail.com> pipeline default-posting-pipeline processing: avoid-duplicates
Jan 09 12:00:58 2021 (1571671) <91B190F7-EEA3-4FA7-9808-2C35774E665A@gmail.com> pipeline default-posting-pipeline processing: cleanse
Jan 09 12:00:58 2021 (1571671) <91B190F7-EEA3-4FA7-9808-2C35774E665A@gmail.com> pipeline default-posting-pipeline processing: cleanse-dkim
Jan 09 12:00:58 2021 (1571671) <91B190F7-EEA3-4FA7-9808-2C35774E665A@gmail.com> pipeline default-posting-pipeline processing: cook-headers
Jan 09 12:00:58 2021 (1571671) <91B190F7-EEA3-4FA7-9808-2C35774E665A@gmail.com> pipeline default-posting-pipeline processing: subject-prefix
Jan 09 12:00:58 2021 (1571671) <91B190F7-EEA3-4FA7-9808-2C35774E665A@gmail.com> pipeline default-posting-pipeline processing: rfc-2369
Jan 09 12:00:59 2021 (1571671) <91B190F7-EEA3-4FA7-9808-2C35774E665A@gmail.com> pipeline default-posting-pipeline processing: to-archive
Jan 09 12:00:59 2021 (1571671) <91B190F7-EEA3-4FA7-9808-2C35774E665A@gmail.com> pipeline default-posting-pipeline processing: to-digest
Jan 09 12:00:59 2021 (1571671) <91B190F7-EEA3-4FA7-9808-2C35774E665A@gmail.com> pipeline default-posting-pipeline processing: to-usenet
Jan 09 12:00:59 2021 (1571671) <91B190F7-EEA3-4FA7-9808-2C35774E665A@gmail.com> pipeline default-posting-pipeline processing: after-delivery
Jan 09 12:00:59 2021 (1571671) <91B190F7-EEA3-4FA7-9808-2C35774E665A@gmail.com> pipeline default-posting-pipeline processing: acknowledge
Jan 09 12:00:59 2021 (1571671) <91B190F7-EEA3-4FA7-9808-2C35774E665A@gmail.com> pipeline default-posting-pipeline processing: dmarc
Jan 09 12:00:59 2021 (1571671) <91B190F7-EEA3-4FA7-9808-2C35774E665A@gmail.com> pipeline default-posting-pipeline processing: arc-sign
Jan 09 12:00:59 2021 (1571671) <91B190F7-EEA3-4FA7-9808-2C35774E665A@gmail.com> pipeline default-posting-pipeline processing: to-outgoing
Jan 09 12:00:59 2021 (1571667) [IncomingRunner] starting oneloop
Jan 09 12:00:59 2021 (1571667) [IncomingRunner] ending oneloop: 0
Jan 09 12:00:59 2021 (1571671) [PipelineRunner] finishing filebase: 1610190058.1544778+e952a743e8df115e8fff9c60f98b189d4800e7e6
Jan 09 12:00:59 2021 (1571671) [PipelineRunner] doing periodic
Jan 09 12:00:59 2021 (1571671) [PipelineRunner] committing transaction
Jan 09 12:00:59 2021 (1571671) [PipelineRunner] checking short circuit
Jan 09 12:00:59 2021 (1571671) [PipelineRunner] ending oneloop: 1
Jan 09 12:00:59 2021 (1571671) [PipelineRunner] starting oneloop
Jan 09 12:00:59 2021 (1571671) [PipelineRunner] ending oneloop: 0
Jan 09 12:00:59 2021 (1571674) [VirginRunner] starting oneloop
Jan 09 12:00:59 2021 (1571674) [VirginRunner] ending oneloop: 0
Jan 09 12:00:59 2021 (1571669) [NNTPRunner] starting oneloop
Jan 09 12:00:59 2021 (1571669) [NNTPRunner] ending oneloop: 0
Jan 09 12:00:59 2021 (1571675) [DigestRunner] starting oneloop
Jan 09 12:00:59 2021 (1571675) [DigestRunner] ending oneloop: 0
Jan 09 12:01:00 2021 (1571670) [OutgoingRunner] starting oneloop
Jan 09 12:01:00 2021 (1571670) [OutgoingRunner] processing filebase: 1610190059.1591551+dcfcb22d5156b0a4d4267eabf83c5bb68f945e41
Jan 09 12:01:00 2021 (1571670) [OutgoingRunner] processing onefile
Jan 09 12:01:00 2021 (1571670) [outgoing] <function deliver at 0x7f612989dea0>: <91B190F7-EEA3-4FA7-9808-2C35774E665A@gmail.com>
Jan 09 12:01:00 2021 (1571664) [ArchiveRunner] starting oneloop
Jan 09 12:01:00 2021 (1571664) [ArchiveRunner] processing filebase: 1610190059.1079752+2644b9a3eab17d52203a2c2648a1db5ff146eb6d
Jan 09 12:01:00 2021 (1571664) [ArchiveRunner] processing onefile
Jan 09 12:01:00 2021 (1571666) [CommandRunner] starting oneloop
Jan 09 12:01:00 2021 (1571666) [CommandRunner] ending oneloop: 0
Jan 09 12:01:00 2021 (1571670) [OutgoingRunner] finishing filebase: 1610190059.1591551+dcfcb22d5156b0a4d4267eabf83c5bb68f945e41
Jan 09 12:01:00 2021 (1571670) [OutgoingRunner] doing periodic
Jan 09 12:01:00 2021 (1571670) [OutgoingRunner] committing transaction
Jan 09 12:01:00 2021 (1571670) [OutgoingRunner] checking short circuit
Jan 09 12:01:00 2021 (1571670) [OutgoingRunner] ending oneloop: 1
Jan 09 12:01:00 2021 (1571670) [OutgoingRunner] starting oneloop
Jan 09 12:01:00 2021 (1571670) [OutgoingRunner] processing filebase: 1610190060.1351898+91420b755194277d1236a36b6e2195eff547c8b0
Jan 09 12:01:00 2021 (1571670) [OutgoingRunner] processing onefile
Jan 09 12:01:00 2021 (1571667) [IncomingRunner] starting oneloop
Jan 09 12:01:00 2021 (1571667) [IncomingRunner] ending oneloop: 0
Jan 09 12:01:00 2021 (1571670) [outgoing] <function deliver at 0x7f612989dea0>: <91B190F7-EEA3-4FA7-9808-2C35774E665A@gmail.com>
...
Jan 09 12:16:41 2021 (1571670) [outgoing] <function deliver at 0x7f612989dea0>: <91B190F7-EEA3-4FA7-9808-2C35774E665A@gmail.com>
...
Jan 09 12:16:41 2021 (1571670) [outgoing] <function deliver at 0x7f612989dea0>: <91B190F7-EEA3-4FA7-9808-2C35774E665A@gmail.com>
...
Jan 09 12:16:41 2021 (1571670) [outgoing] <function deliver at 0x7f612989dea0>: <91B190F7-EEA3-4FA7-9808-2C35774E665A@gmail.com>
...
Jan 09 12:16:41 2021 (1571670) [outgoing] <function deliver at 0x7f612989dea0>: <91B190F7-EEA3-4FA7-9808-2C35774E665A@gmail.com>
...
Jan 09 12:16:41 2021 (1571670) [outgoing] <function deliver at 0x7f612989dea0>: <91B190F7-EEA3-4FA7-9808-2C35774E665A@gmail.com>
...
Jan 09 12:16:42 2021 (1571670) [outgoing] <function deliver at 0x7f612989dea0>: <91B190F7-EEA3-4FA7-9808-2C35774E665A@gmail.com>
...
Jan 09 12:16:42 2021 (1571670) [outgoing] <function deliver at 0x7f612989dea0>: <91B190F7-EEA3-4FA7-9808-2C35774E665A@gmail.com>
...
Jan 09 12:16:42 2021 (1571670) [outgoing] <function deliver at 0x7f612989dea0>: <91B190F7-EEA3-4FA7-9808-2C35774E665A@gmail.com>
...
Jan 09 12:16:42 2021 (1571670) [outgoing] <function deliver at 0x7f612989dea0>: <91B190F7-EEA3-4FA7-9808-2C35774E665A@gmail.com>
...
Jan 09 12:16:42 2021 (1571670) [outgoing] <function deliver at 0x7f612989dea0>: <91B190F7-EEA3-4FA7-9808-2C35774E665A@gmail.com>
...
...
Jan 09 14:06:30 2021 (1601275) [outgoing] <function deliver at 0x7f038df80ea0>: <91B190F7-EEA3-4FA7-9808-2C35774E665A@gmail.com>
...