[plug] Sendmail return address mangling?

[Greg Mildenhall]

On Thu, 24 Dec 1998, Colin 't Hart wrote:
> Can someone give me a basic rundown on why one would want
> sendmail (or any other MTA) to mangle the return addresses
> of emails?
When you sent the email to the list, your mailer did not realise it was
sending it to a list. It sent a normal email as if it was to a user called
"plug" at linux.org.au. The reply-to address is set to your email address.
When the listserver recieves it, it has two choices:
a) bounce the mail on exactly as it was recieved, changing only the "To"
   field.
b) resend the mail with the to field altered, and with the Reply-to field
   set to "plug at linux.org.au"

When people get the mail, the Reply-to address will either be your
address, or it will be the address of the list. If they reply to the
message, this will determine the (defualt) address to which the reply will
go. Some people would prefer it to go to the list so that everyone sees
the reply, others would prefer it to go to the author to keep traffic down
on the list. It's a matter of taste, mostly, and either way, the person
replying can override it.

> My uninformed opinion would be to leave the return address as what
> the use put on the email, just like Australia Post leaves your
> return address intact when you write it on the back of your envelope.
If you were moving house, you might put a "munged" return address on the
letter, so that the reply would go to your new address. In the online
example, Australia post (the list-server) changes it for you, because your
mail-client doesn't know what's going on.

> Or does the email vs snail mail comparison not extend so far?
No, probably not. Australia Post doesn't have a service whereby they
photocopy your mail and send it to everyone on a list.

> Do firewalls affect the picture? 
No. Well, they don't affect the rationale or the efficacy of
reply-munging, anyway. I find it difficult to envisage a firewall that is
affected by, or affects, Reply-to addresses.

> What about when the mail server is inside the firewall? 
> The firewall also needs to act as a mail server in this case, right?
These are issues that will determine whether mail gets through at all,
they probably don't relate to reply-munging.

> PS Why I ask? Where I work the sendmail.cf is setup this way, AFAIK
It is? In what way? What does it change the reply-to address to?
Generally, only mailing list change reply-to, corporate mailservers that
mung things in sendmail.cf usually are trying to make replies come back to
a different server to which the original mail was sent from. They
typically handle this by munging the From field, not the Reply-to field.

Hope some of this is useful. Hope noone thinks this is a specific example
of why replies shouldn't go to the list. :)

-Greg Mildenhall