Canonical Problem

Hi List,

I have 2 domains @example.com and @mysite.com

I have configured sender_canonical file with this rule:
@example.com     @mysite.com

so when a user with domain @example.org sends an e-mail,
in the FROM field of the receiver will be @mysite.com .

(for example  there are 2 usres:
[email protected]     and     [email protected]

when alice sends e-mails, her address becomes [email protected].

Now my problem is when Alice is the "receiver" not the sender.  i.e if
[email protected] sends an email to Alice postfix will look for
[email protected] instead of [email protected] and probably this email
will never be sent, because [email protected] doesn't exist.

So how can I say postfix to not change the address in the "TO" field??

Is it indifferent to use canonical or sender_canonical?