Thank you for pointing this out. I am no way expert but trying to study and understand. I then found other negative comments regarding the lack of DMARC, while on posteo website they say: “We have a DMARC “none” policy for Posteo email domain names, since DMARC is currently not recommended for mailbox providers. Outbound DMARC policies are primarily “best-suited for transactional emails and semi-transactional emails” (dmarc-org FAQ). At the present, DMARC has implications which do not meet customers’ individual use of email.” link

The dmarc-org FAQ is interesting too. I understand that Posteo publishes thier DMARC record, if I am not wrong

I would appreciate your opinion, you seem competent! Thank you

Thank you, very useful. For some reason Posteo is not on the list