How to disable plain text authentication on mail server

Disabling plain text authentication on a mail server is an important security measure to prevent unauthorized access to email accounts. Here are the general steps to disable plain text authentication on popular mail servers:

1. Postfix (Linux)

In the /etc/postfix/main.cf file, add the following lines:

smtpd_passwords = shadow
smtpd_sasl_type = dovecot
smtpd_sasl_path = /var/lib/dovecot/login

Then, restart the Postfix service:

sudo service postfix restart

2. Sendmail (Linux)

In the /etc/sendmail.cf file, add the following lines:

O AuthenticationMechanisms=CRAM-MD5, DIGEST-MD5
O PlainAuthenticationRejectionMessage = "Authentication failed"

Then, restart the Sendmail service:

sudo service sendmail restart

3. Microsoft Exchange (Windows)

In the Exchange Management Console, navigate to Server Configuration > Client Access > Authentication. Uncheck the box next to Plain Text Authentication.

4. Dovecot (Linux)

In the /etc/dovecot/dovecot.conf file, add the following lines:

auth_mechanisms = plain login cram-md5 digest-md5

Then, restart the Dovecot service:

sudo service dovecot restart

5. Cyrus IMAP (Linux)

In the /etc/cyrus-imapd/cyrus.conf file, add the following lines:

auth_mechanisms = cram-md5 digest-md5

Then, restart the Cyrus IMAP service:

sudo service cyrus-imapd restart

6. OpenSMTPD (FreeBSD)

In the /etc/mail/smtpd.conf file, add the following lines:

auth_type = cram-md5
auth_mechanisms = cram-md5

Then, restart the OpenSMTPD service:

sudo service smtpd restart

Important notes:

• Before disabling plain text authentication, ensure that you have alternative authentication mechanisms enabled, such as CRAM-MD5, DIGEST-MD5, or OAuth.
• Disabling plain text authentication may break compatibility with some email clients or applications that rely on it.
• It's recommended to test your email server configuration after making these changes to ensure that authentication works correctly.

Remember to always follow best practices for securing your email server, including enabling SSL/TLS encryption, using strong passwords, and regularly updating your server software.