[exim] need to rewrite _ characters in MAIL FROM domain part

Hi,

I seem to have some apps that are sending with a underscore in
the domain part. Searching the exim-user archives suggests that
I can work around this by rewriting the MAIL FROM address,
replacing the domain part _ chars with . chars.

Can anyone offer a rewrite rule that will do this? I'm going
to try to figure it out myself now, but for someone more versed
in rewriting rules, this may be trivial.

Thanks,

Dave

-- 
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  Dave Lugo     dlugo@???      No spam, thanks.
  Are you the police?  . . .  No ma'am, we're sysadmins.
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