I ran into this problem as well and in the end added a separate field for the normalized (lowercase) form with a uniqueness check on that. Users would still be

I ran into this problem as well and in the end added a separate field for the normalized (lowercase) form with a uniqueness check on that. Users would still be presented the original case and it would be preserved when sending e-mails but for identification/uniqueness purposes e-mails were considered case insensitive.