How to configure sendmail for outgoing mail only

To configure Sendmail for outgoing mail only, you'll need to modify the Sendmail configuration file (sendmail.cf or sendmail.mc) to restrict its functionality to only sending mail and not accepting incoming mail.

Here are the general steps:

Step 1: Create a new configuration file

Create a new file, e.g., sendmail.mc, in the /etc/mail directory (or the equivalent directory on your system). This file will contain the modified configuration.

Step 2: Restrict incoming mail

Add the following lines to the sendmail.mc file to restrict incoming mail:

define(`confSMTP_ACCEPT_MAX', `0')dnl
define(`confSMTP_ACCEPT_MIN', `0')dnl
define(`confSMTP_ACCEPT', `no')dnl

These lines set the maximum, minimum, and default values for incoming mail to 0, effectively disabling incoming mail acceptance.

Step 3: Configure outgoing mail

Add the following lines to the sendmail.mc file to configure outgoing mail:

define(`confSMTP_SEND', `yes')dnl
define(`confSMTP_RELAYHOST', `your_smtp_server')dnl

Replace your_smtp_server with the hostname or IP address of your SMTP server (e.g., your mail server or a third-party SMTP service).

Step 4: Update the Sendmail configuration

Run the following command to update the Sendmail configuration:

make -f /etc/mail/sendmail.mc sendmail.cf

This will generate a new sendmail.cf file based on the modified sendmail.mc file.

Step 5: Restart Sendmail

Restart the Sendmail service to apply the new configuration:

service sendmail restart

Alternatively, you can use the sendmail command with the -q option to reload the configuration:

sendmail -q

Verify the configuration

To verify that Sendmail is now configured for outgoing mail only, you can use the sendmail -bv command to test the configuration:

sendmail -bv [email protected]

If everything is set up correctly, Sendmail should send a test email to the specified address.

That's it! Your Sendmail configuration should now be restricted to only sending outgoing mail.