Hi @Mark. Sorry for the delay. I have been out with another Glide prospect!
Unfortunately I can’t test this again at the moment as I have no spare Pro licences. They are all allocated to customers so I cannot create a test app with email whitelist. However I can drop an email input on a form and submit. That certainly does not lowercase the email. It leaves it as with any uppercase in place.
This issue I was having related to login but also to matching when used in a relation. It seems that the match is case-sensitive and so would fail if the email in one sheet did not match the case of the email in its relation sheet.
For most relations this is not an issue as I always use a RowId (so that I can modify any other column content without breaking the link) but with users we are forced to use the email.
Does this help?