Sendmail can block outgoing email addresses and prevent unnecessary email transmission. Bobcares, as a part of our Server Management Services, offers solutions to your queries.

Sendmail Block Outgoing Email Address | How?

Sendmail provides many options for blocking an email address, domain name, or IP address using an access database. The access control for the Sendmail SMTP server will be /etc/mail/access file. We can use this file to specify whom we accept mail from, whom we accept relaying from, and whom we will not send to, among other things.

Overwriting the “From:” field of an outgoing email message can be useful at times. For say, if we have a web-based app that sends emails. Normally, the mail message would appear to be sent by the user who was in control of the web server process. We might want to specify a different source address so that the mail appears to have come from a different user or address on that machine. We may also need to sometimes block some outgoing email addresses. Sendmail provides a mechanism for specifying which system users should be granted this ability.

The steps to use Sendmail to block outgoing email addresses are as follows:

• Firstly, set up Sendmail.

  # vi /etc/mail/sendmail.cf
• Check that the following line exists in your configuration file. If not present, we’ve to include it.

  FEATURE(`access_db’)dnl
• Exit the shell prompt after saving the file. Open the /etc/mail/access file now:

  # vi /etc/mail/access
• We can use the following format to block junk or spam emails.

  spam@domain.com REJECT

  192.168.1.100 REJECT

  202.54.1.100/255.0.0.0 REJECT
• Save the document. If we make changes to sendmail.mc or the access file, we must regenerate /etc/mail/sendmail.cf or rebuild the access database. Enter any of the following commands:

  # cd /etc/mail
  # make

  # m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf

   
• Finally, restart Sendmail.

  # /etc/init.d/sendmail restart

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Conclusion

Sendmail has many useful configurations. One such configuration is provided by our Support team that can be set up in Sendmail to block the outgoing email address.