[exim] conditional delivery (according to recipients)

hello,

i want to make conditional delivery of e-mails, depending on
destination, not source (which would be trivial task to fill with a
local_domains...).

basic requirement is that all the mails for somebody@??? should
be proceeded locally (as it is now), but all others should be forwarded
to our external SMTP server, because some portals started to reject our
postings due to their new, paranoid spam control policies. all addresses
with dot in username (including name.surname@???) should also be
forwarded.

moreover it should be good to check if sender address in forwarded mails
is in form somebody@??? (without dot in username) and change it
to reply@??? if yes. i can live without it, but this could ease
the pain of using e-mail for our users.

i'm using exim 3.36 on Debian Sarge if that matters. i'm a littlle
skilled in administration in general, but not very familiar with mail
delivery configuration, so i can probably understand even just hints,
but treat me as newbie please. =}

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