Does Mailman generally send email with a null sender?
This is what I see in the log:
Jun 28 02:37:45 2020 (14588) ('127.0.0.1', 52726) handling connection Jun 28 02:37:45 2020 (14588) ('127.0.0.1', 52726) Data: b'LHLO mail.example.coop' Jun 28 02:37:45 2020 (14588) ('127.0.0.1', 52726) Data: b'MAIL FROM:<>' Jun 28 02:37:45 2020 (14588) ('127.0.0.1', 52726) sender: <> Jun 28 02:37:45 2020 (14588) ('127.0.0.1', 52726) Data: b'RCPT TO:<techque-bounces@example.org>' Jun 28 02:37:45 2020 (14588) ('127.0.0.1', 52726) recip: techque-bounces@example.org Jun 28 02:37:45 2020 (14588) ('127.0.0.1', 52726) Data: b'DATA' Jun 28 02:37:45 2020 (14588) ('127.0.0.1', 52726) Data: b'QUIT'
Notice the empty MAIL FROM.
Sendgrid seems to be choking on that because it needs to check if sending domain has been validated. If there is no sending domain it seems to reject.
Why does Mailman do this? Can it be changed? I've been trying to find the relevant section of the code to no avail.