RFC 822 calls for the "local-part" to be case-preserved. It also specifies that the special address, "Postmaster", must be deliverable with any combination of

RFC 822 calls for the "local-part" to be case-preserved. It also specifies that the special address, "Postmaster", must be deliverable with any combination of case used. I do see, however, that RFC 5321 not only reinforces the idea that the case of the "local-part" must be preserved, but it explicitly declares that "smith" and "Smith" may very well be different recipient mailboxes, which is brain-damaged, given that those are very often typed in by fallible humans.