Sendmail help sought

[Timothy Murphy]

Tim wrote:

> I'm not talking about IP addresses, I mean email addresses.  Presume
> that I am tim at localhost on my machine, and I masquerade my mail to
> change localhost to the domain name of my ISP (e.g. example.com), and I
> (now) send out my mail as tim at example.com, to save me from configuring
> my mail clients.  But, *I* shouldn't do that, because I am not user
> "tim" on my ISP, some other person has that ISP mail account.

That is exactly my problem.
I am "tim" on my own machines, but "gayleard at eircom.net" to my ISP.

> Masquerading has to be done with due care, as with just about all
> aspects of running a mail server attached to the public internet.

I must admit I am still not clear about the purpose of masquerading.
What is a concrete situation where it might make sense?

Incidentally, I don't think I am running a mail SERVER
as I understand that term.
I collect all my email from external mail servers with fetchmail .


-- 
Timothy Murphy  
e-mail: gayleard /at/ eircom.net
tel: +353-86-2336090, +353-1-2842366
s-mail: School of Mathematics, Trinity College, Dublin 2, Ireland