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sendmail and isp smart host

I am trying to setup my sendmail for sending emails throught my linux box

I can send and recieve email for all local acounts BUT when i am sending email to the internet to other user i keep taking the error message

"Domain ofe sender address root@linux.mydomain.com does not exit or resolve"

I am taking this message from my ISP mail server

As far as i am consern this is right because the ISP does not know my domain at linux box
What to do

My user name is root
my host is linux
and my domain is mydomain.com

I have try a lot of stuff but still is not working

Can anyone help me Please

If you don't have a real domain-name it is normal behavior for ISPs to prevent spam. Take a look at /etc/mail/sendmail.cf and see if setting the Dj$w in:

Quote:

# define this only if sendmail cannot automatically determine your domain
#Dj$w.Foo.COM

to your ISP domain, solves your problem.
Another solution is to get a no-ip.com (or similar) domain if you're on a dynamic IP.

"Domain ofe sender address root@linux.mydomain.com does not exit or resolve"

You are correct, your ISP's MTA (smart host) is testing the sender address sent by your MTA (probably the envelope sender) and it cannot resolve this to a name or IP.

The way I see it, you have a couple of choices:

1) Configure your MUA to set the proper sender address address. Possibly by setting the reply-to
2) Configure sendmail to masquerade as a valid domain name that can be looked up by your ISP's MTA.

If your using Redhat, see /etc/mail/sendmail.mc and look for the section regarding...

Code:

dnl # The following example makes mail from this host and any additional

dnl # specified domains appear to be sent from mydomain.com 

dnl # 

dnl MASQUERADE_AS(`mydomain.com')dnl

dnl # 

dnl # masquerade not just the headers, but the envelope as well

dnl #

dnl FEATURE(masquerade_envelope)dnl

If you're not using Redhat, then you can add the MASQUERADE_AS and FEATURE statments above to your sendmail.mc file and change to meet the requirements of your ISP's MTA.

i already have masquarade the domain and also the From address but still not working

in the mail log i take root@mydomain.com when i sent an external email and interna also but

because the internal emai to another user i can rea it the masquarade and the From is working fine

but for external email i dont know what is going on