Postfix/Exim sender address rewriting (was: Postfix ... ComCast port 587)

[Bruce Dawson]

Ben Scott wrote:
> On Tue, Jan 20, 2009 at 12:02 PM, Ben Scott <dragonhawk at gmail.com> wrote:
>   
>>  ... Sendmail ... /etc/mail/genericstable:
>>        bscott  dragonhawk at gmail.com
>>
>>  I presume Postfix has a similar capability.  Exim may as well.  Anyone?
>>     
>
>   I'm disappointined nobody has posted an answer to the above.  I'm
> changing the subject line and reposting to try and call attention.
> This seems like a real useful thing to know how to do.  For me, for
> others reading, for the list archives.
>   

Grumble. It depends on how you have your mail set up.
>   The goal here is to configure one's MTA (Mail Transfer Agent) such
> that mail from a local-only email address gets rewritten to an valid
> public Internet email address.  For example, on my home PCs, my *nix
> username is <bscott>.  If I send mail from a local program, the
> sending email address generally becomes something like
> <bscott at blackfire.bscott.local>.  That's obviously not going to be
> useful on the Internet.  So I have configure my MTA (which happens to
> be Sendmail) to re-write those to be <dragonhawk at gmail.com>, which is
> my public address.
>
>   How does one do this in Postfix and/or Exim?
>   

Assuming:

* Postfix
* Your computer is sending mail using comcast as the ISP. (Typical home
set up.)
* Ubuntu 6.10 (Edgy Eft) - I know its old, but its what I have up and
handy at the moment

In /etc/postfix/main.cf make sure you have the following line:

myhostname = c-99-999-999-999.hsd1.nh.comcast.net

(replacing the '9's with your reversed comcast issued IP address).

Note: I believe this will work. It works on this system, but I'm
forwarding via postfix all my mail for delivery by another system. Your
mileage is likely to vary. Also, I believe you can use *any* valid
domain there; I don't think comcast does double-reverse lookups on the
this name (but they should).

I'm sure others on the list will correct me if I'm wrong.
> -- Ben
>
>   
--Bruce