I discovered an issue with sending print jobs to my HP8600 by email when the sender whitelist.
HP's eprint service appears to use either the Return Path or the Envelope-from address in the email's SMTP header (probably the "Envelope-from" as it would be silly to use Return path).
The trouble is, sometimes these are not always the same as the "From" address, depending on the type of mail system.
For example, my son's school email adress is say john.doe@hisschool.com and his From address in the SMTP header is john.doe@hisschool.com but when I whitelist that address for my printer it doesn't work when he sends a print job.
Inspection of the SMTP header from one of his emails shows the Return Path and Envelope-from is:
pvrs-20196318c=john.doe@hisschool.com
Now if I put that email address into the whitelist it works - he can send to the printer and it will print.
There's just one problem - that numerical code in front of his email address appears to change occasionally. Given that I bought this printer specifically so my kids can print from their school notebook computers (because they can't install drivers on them) this is quite a disappointing discovery ...