Blocking off mail can also involve legal and ethical issues, depending on your situation. The senders could claim that blocking their messages was a violation of their rights to free speech. Public institutions, such as a university, would probably be held to a higher standard than a private company. Other New Security Features sendmail has the ability to run a program to act on incoming mail on a user's behalf. One example is the vacation program, which stores the received e-mail and immediately replies with a message.
Users can also write their own.
This feature can be enabled by commenting out the Mprog line in the sendmail . The .forward file is used to forward mail or run programs on the user's behalf, as mentioned above. If the file is writeable by other users, the mail may be intercepted. To counter that, uncommenting the UnsafeGroupWrites line in the configuration file will cause sendmail to reject the .forward file if it is group or world writeable and it contains a program. If the file contains a forwarding address, it works unimpeded.