[exim] Wishlist item: specify error codes in ACL.

I'd like to be able to specify an error code in an ACL when rejecting
mail. For example:

    deny    errorcode = 551
        message = "You are publishing an SPF record but I would have to forward the mail to <$acl_m9>"
        condition = ${if !eq{$acl_m9}{} {1}}

The same should be possible for deferral too.

I don't actually see RFC1893/RFC2034 ENHANCEDSTATUSCODES on the wishlist
either, for that matter.

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dwmw2