Controlling Spam with Linux and Greylisting

Description

Do you manage your own email systems? Then greylisting is for you.

Those who send out junk emails make money when people open and respond to those emails. They need to get that junk email sent and opened as fast as possible, because they know that after a short period of time, their emails will be marked as junk mail and will be automatically moved by email providers into people’s junk folders.

Hackers and those with bad intentions also send out bulk emails. They find a vulnerability and send out bulk emails hoping that someone will click on an email link and expose themselves to the security flaw.

If you’re in one of these groups (sending out hundreds of thousands or millions of bulk emails in one bunch), then your systems are designed for throughput. These bad actors send their payloads out into the world using their lists of millions of emails, and if they get no response by a defined time limit or get a retry later message, then they skip that email and move on to the next in their list. Depending on whether spammers want to make their process as fast and efficient as possible (time is money to them), they may also remove email addresses from their list that are not able to receive email instantly.

Email greylisting is a method to lower the amount of spam and junk mail that gets into your email inbox. It works by slightly delaying the emails being received and forcing the sender to resend the emails.

If this sounds interesting to you, then jump into this course to see if it can help cut down your spam and increase the security of your email systems.