If you have got a statically assigned IP number, you should not need to adjust anything from the default. Set your host name up as your assigned Internet name and sendmail will do the rest.
If you have got a dynamically assigned IP number and use a dialup PPP connection to the Internet, you will probably be given a mailbox on your ISPs mail server. Lets assume your ISPs domain is example.net, and that your user name is user. Lets also assume you have called your machine bsd.home and that your ISP has told you that you may use relay.example.net as a mail relay.
In order to retrieve mail from your mailbox, you will need to install a retrieval agent. Fetchmail is a good choice as it supports many different protocols. Usually, POP3 will be provided by your ISP. If you have chosen to use user-PPP, you can automatically fetch your mail when a connection to the 'net is established with the following entry in /etc/ppp/ppp.linkup:
MYADDR: !bg su user -c fetchmail
If you are using sendmail (as shown below) to deliver mail to non-local accounts, put the command
!bg su user -c "sendmail -q"
after the above shown entry. This forces sendmail to process your mailqueue as soon as the connection to the 'net is established.
I am assuming that you have an account for user on bsd.home. In the home directory of user on bsd.home, create a .fetchmailrc file:
poll example.net protocol pop3 fetchall pass MySecret
This file should not be readable by anyone except user as it contains the password MySecret.
In order to send mail with the correct from: header, you must tell sendmail to use firstname.lastname@example.org rather than email@example.com. You may also wish to tell sendmail to send all mail via relay.example.net, allowing quicker mail transmission.
The following .mc file should suffice:
VERSIONID(`bsd.home.mc version 1.0') OSTYPE(bsd4.4)dnl FEATURE(nouucp)dnl MAILER(local)dnl MAILER(smtp)dnl Cwlocalhost Cwbsd.home MASQUERADE_AS(`example.net')dnl FEATURE(allmasquerade)dnl FEATURE(masquerade_envelope)dnl FEATURE(nocanonify)dnl FEATURE(nodns)dnl define(`SMART_HOST', `relay.example.net') Dmbsd.home define(`confDOMAIN_NAME',`bsd.home')dnl define(`confDELIVERY_MODE',`deferred')dnl
Refer to the previous section for details of how to turn this .mc file into a sendmail.cf file. Also, do not forget to restart sendmail after updating sendmail.cf.