SB> If I send a mail to bortzmeyer@foo.bar when the main domain is
    SB> dot.bar and I have in the virtusertable:
    SB> bortzmeyer@foo.bar bortzmeyer
    SB> the mail is received with a header:
    SB> To: bortzmeyer@dot.bar
    SB> which is not what the customer wants.
What else do you have in your .mc ?  Masquerading options maybe?  Out
of the box with no other options sendmail should leave the header to
alone.
cheers,
BM