System Architecture: Intel
RedHat Release: RHL 5.1 (Manhattan)
FAQ Category: Email
Modification Date: Oct 19, 1998

Question:

How do I setup sendmail to masquerade as my ISP when I am on a Dynamic IP
PPP link (e.g., a laptop).  This way you can send mail via shell
scripts (e.g., to your pager).

Answer:

su - root
edit:  /usr/lib/sendmail-cf/cf/redhat.mc
       add:
          MASQUERADE_AS('your mail host')
          FEATURE(masquerade_envelope)

run the following:
    pmake redhat.mc
    mv /etc/sendmail.cf /etc/sendmail.cf.sav
    mv obj/redhat.cf /etc/sendmail.cf
    /etc/rc.d/init.d/sendmail restart

Also:  note that one should have the SAME account on their
Linux box as on their ISP or replies will bounce at the ISP.

References:

several great mails on the redhat-list about 6 months ago