Email rejected (openspf.org) envelope address email@example.com become user40domain.com
an email domain blocked my email with message:
mail.xxxxxx.com rejected a message that claimed an envelope sender address of user40domain.com
mail.xxxxxx.com received a message from mail.domain.com (my public ip) that claimed an envelope sender address of user40domain.com.
The domain user40domain.com has not published an SPF policy. It is possible that the receiving mail server refuses all mail from domains that do not have an SPF policy.
we hosting dns and i already confirm they already use SPF policy, the strange is user40domain.com, it suppose to be firstname.lastname@example.org
any advice ?