Hi,
This is probably a bit OT, but here goes.
I've been running our local school's mail server since 2013, with mail addresses for school staff and some teachers. The server is running CentOS 7 with Postfix and Dovecot, and it's a nice no-bullshit configuration with SPF, DKIM and DMARC.
The school sends quite a lot of email out to parents, and sometimes, mail gets rejected:
--8<-------------------------------------------------------- xxxxxxxx@orange.fr: host smtp-in.orange.fr[193.252.22.65] said: 550 5.2.0 Mail rejete. Mail rejected. ofr_506 [506] (in reply to end of DATA command)
yyyyyyyy@wanadoo.fr: host smtp-in.orange.fr[193.252.22.65] said: 550 5.2.0 Mail rejete. Mail rejected. ofr_506 [506] (in reply to end of DATA command) --8<--------------------------------------------------------
This happens randomly with the usual suspects among crappy mail providers like Orange, Hotmail/Live, Yahoo and the rest.
The school's not happy because in their eyes I'm faulty of badly maintaining their mail server.
In recent years I've got the impression that the big players do everything to make people move to their platform and stop providing their own email systems. And being the admin of email systems can be a real PITA these days.
What can be helpful is to check the reputation of your own servers with services of some big player like https://talosintelligence.com/ and if all is ok, it's a good reason to report to those who think it's your fault.
Regards, Simon