General question regarding rewriting of mail headers,...how does it work...

[Walter Tautz <wtautz@math.uwaterloo.ca>]

Ok. I may not make much sense...
(NOTE. I am not trying do anything particular, just wondering about
the general idea of rewriting).

When sending mail in the following way:


Host1 ------->Host2


and we want it to appear to come from Host3. 


Can Host1 rewrite a message header and then send it to Host3?


Isn't possible that the Host2 smtp server would first do a host lookup
or some kind of comparision from where the message arrived versus what the
mail header says and reject if they aren't the same??

I guess I am asking isn't
possible that the mail server on Host2 will not accept rewritten message
headers. Perhaps I misunderstanding the concept of rewriting...a clarification
from a mail guru in down to earth language or a good weblink would be appreciated.


-walter