Debian OS can send email or even host an email server for facilitating email services to the organization. Since we are dealing with email, there are a lot of possible vulnerabilities introduced via email. This section guides you on how to harden Debian email mailer.
These are the identified threats related to Debian software.
By default, email mailer isn ot using SSL/TLS to fetch email across Internet.
Here are the list if actions to counter the issues.
Since there are different kinds of mailers, one should configure all mailers to only use SSL/TLS connection.
That's all for hardening Debian by hardening email mailer.