[exim] how to replace To: field with list of real recipients

Hi, people!
Some MTA's checks "To:" field for adreess this MTA serving. In case when "To:"
doesn't contains an address this MTA serving (for example, "To:" contains an
local alias that points to remote address) message is rejected. I think it is
good idea to replace "To:" field with list of real recipients to prevent
fails of delivery messages to such kind of MTA's. Actually I got some problem
with doing this. Namely, how to access to recipients list
in "headers_rewrite"?