[exim] Rewrite rule message

HI everyone,

i'm trying to rewrite the From field for all my messages that comes to my
exim server.
Here is my rule:
*@*.lutix.org $1@???

and then for example:
exim -brw ftg@???

  sender: ftg@???
    from: ftg@???
      to: ftg@???
      cc: ftg@???
     bcc: ftg@???
reply-to: ftg@???
env-from: ftg@???
  env-to: ftg@???

but when i send and email to gmail, the From field is "ftg,,," instead of
"ftg". What are the commas for?

Thanks