OK, this has been bugging me for a while now.
2822 says that the domain-part of an address is interpreted as a
domain name, and the DNS RFCs say domain names are case-insensitive.
But it looks to me like 2822 is silent on *local-part* case sensitivity.
Logic can take us either way; i.e., since RFCs are generally silent
unless insensitivity is needed, local-part must be sensitive--or,
alternately, since the RFC is silent in this case it's best to
interpret for maximum compatibility, so local-part must be insensitive.
And most MTAs and MUAs in my experience treat local-part as case
Except Apple Mail S/MIME processing. All other S/MIME MUAs I've
tested go with case insensitive for S/MIME local-part address
matching--but Apple Mail is case sensitive. This is a real pain in
my neck, especially with the DoD PKI, where email addresses are not
(yet) centrally provisioned, so case mismatches between the mail
system and the PKI are common.
I can't get Apple to budge on fixing it because they've staked out
the strict interpretation, despite the common interpretation
otherwise and the demonstrable problems this causes. A fix 2822
would help, but I figured I'd ask the opinion of this list before I
took things further:
Should the local-part of an RFC2822 addr-spec be interpreted as case-
Description: S/MIME cryptographic signature