I am receiving the error message “Blocked GENERIC rDNS” – What does that mean?
Due to recurring massive spam abuse from exploited hosts, Cleanmail.ch only accepts mail from correctly defined, non generic rDNS/PTR entries for hosts in cloud services / dedicated servers / VPS / certain IP ranges.
This sender server has a generic PTR in the upstream provider’s domain.
We recommend setting the PTR (and SMTP HELO) to a non generic hostname in a domain managed by the server operator.