How can I get Exim to strip the hostname from the sender's address?

I have Exim configured to remove the hostname portion of the domain on outgoing mail, and yet the hostname is present when the mail gets delivered.

I want to rewrite local addresses in mail that goes to the outside world, but not for messages that remain within the local intranet.

I'm using this rewriting rule to change login names into “friendly” names, but if mail comes in for an upper case login name, it doesn't get rewritten.

*@my.domain      ${lookup{$1}dbm{/usr/lib/exim/longforms}\
$value}fail}@my.domain bcfrtFT

The longforms database has entries of the form:

ano23: A.N.Other

Is it possible to completely fail a message if the rewrite rules fail?

I'm using $domain as the key for a lookup in a rewriting rule, but its contents are not being lowercased. Aren't domains supposed to be handled caselessly?

I want to rewrite local sender addresses depending on the domain of the recipient.

I want to rewrite recipient address depending on the domain of the sender.