executing the following command:m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cfThe default configuration which ships with Red Hat Enterprise Linux works for most SMTP-onlysites. However, it does not work for UUCP (UNIX to UNIX Copy) sites. If using UUCP mailtransfers, the /etc/mail/sendmail.mc file must be reconfigured and a new/etc/mail/sendmail.cf must be generated.Consult the /usr/share/sendmail-cf/README file before editing any files in the directoriesunder the /usr/share/sendmail-cf directory, as they can affect the future configuration of/etc/mail/sendmail.cf files.3.1.4. MasqueradingOne common Sendmail configuration is to have a single machine act as a mail gateway for allmachines on the network. For instance, a company may want to have a machine calledmail.example.com that handles all of their email and assigns a consistent return address to alloutgoing mail.In this situation, the Sendmail server must masquerade the machine names on the companynetwork so that their return address is user@example.com instead of user@host.example.com.To do this, add the following lines to /etc/mail/sendmail.mc:FEATURE(always_add_domain)dnl FEATURE(`masquerade_entire_domain')FEATURE(`masquerade_envelope') FEATURE(`allmasquerade')MASQUERADE_AS(`bigcorp.com.') MASQUERADE_DOMAIN(`bigcorp.com.')MASQUERADE_AS(bigcorp.com)After generating a new sendmail.cf using m4, this configuration makes all mail from inside thenetwork appear as if it were sent from bigcorp.com.3.1.5. Stopping SpamEmail spam can be defined as unnecessary and unwanted email received by a user who neverrequested the communication. It is a disruptive, costly, and widespread abuse of Internetcommunication standards.Sendmail makes it relatively easy to block new spamming techniques being employed to sendjunk email. It even blocks many of the more usual spamming methods by default.For example, forwarding of SMTP messages, also called relaying, has been disabled by defaultsince Sendmail version 8.9. Before this change occurred, Sendmail directed the mail host(x.edu) to accept messages from one party (y.com) and sent them to a different party (z.net).Chapter 11. Email192
