If this is true and Apple's service does leave out a "from" header (it may just as well be a parse error somewhere on the website's side) that would definitely be on the mail forwarding service, not on this particular website.
RFC 5322 and RFC 2822 specify that at least and at most one From: header must be present. Mail services that don't add at least some kind of fake From header aren't spec compliant and should probably expect error and delivery problems. RFC 2822 is over 20 years old now.
In theory Apple's service could only be RFC 822 compliant, but this does pose a big interoperability problem for its customers.
Comments
It's not a "bad user doing bad things," it's a widely-used email forwarding service.
If this is true and Apple's service does leave out a "from" header (it may just as well be a parse error somewhere on the website's side) that would definitely be on the mail forwarding service, not on this particular website.
RFC 5322 and RFC 2822 specify that at least and at most one From: header must be present. Mail services that don't add at least some kind of fake From header aren't spec compliant and should probably expect error and delivery problems. RFC 2822 is over 20 years old now.
In theory Apple's service could only be RFC 822 compliant, but this does pose a big interoperability problem for its customers.