[MM3-users] 501 Message has defects

Hi

I'm using GNU Mailman 3.3.8 (Tom Sawyer) on debian 12, and I have this issue on a scheduled e-mail, every day:

2024-10-25T04:00:04.874081+01:00 XXXXXXX postfix/lmtp[29258]: CEB32100F44: to=<XXX@XXX.XX>, relay=localhost[127.0.0.1]:8024, delay=0.02, delays=0.01/0/0.01/0.01, dsn=5.0.0, status=bounced (host localhost[127.0.0.1] said: 501 Message has defects (in reply to end of DATA command))

I have already changed some settings on the postfix and list configurations, without success. Outlook 365 and gmail receive the email without issues.

Does anyone have any idea of how I can fix this?

Thanks,