Harden Postfix to block spammers

Configure Postfix to block spam before it enters the server

Sep. 10, 2019 - Willem L. Middelkoop

This month I had to deal with backscatter spam, affecting one of the mail servers I manage. As server engineer I make sure that servers don't send spam and that incoming email gets filtered. Despite all good efforts, this server kept being blacklisted for sending spam to iCloud, Office 365 and Google Gmail for Business (G Suite). Read along to find out how what caused this and how to fix this.

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Implementing stringent SMTP restrictions in Postfix - annotated screenshot from main.cf

Prevent backscatter bounce messages by responding with SMTP error codes instead

Simple backscatter scenario, mail server bounces message to a falsified sender address

Prevent backscatter spam by checking all messages before forwarding them to another server

Causing backscatter spam when the first mail server forwards email to another server that blocks message

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Articles (155)

2024-12-19 Data versus Feeling
2024-12-09 The Problem With Bitcoin
2024-11-11 Write your own words
2024-11-10 Go Viral on X
2024-10-20 Marathon
2024-09-10 I see dead people
2024-05-11 Developing a native iOS app
2024-03-24 Half Marathon
2024-03-05 No, I Won't Build That!
2024-02-16 Vision Pro
2024-01-16 Health and fitness data
2023-12-15 Backup Rotation Scheme
2023-11-10 Apple Watch as Phone
2023-11-01 And... there is light!
2023-10-14 Giving AI Training
2023-10-13 Hello, stranger
2023-08-23 The Same, Differently
2023-05-31 Impact of training
2023-05-08 Tablet as Tool
2023-05-03 Using AI to generate code
2023-05-01 Working Offline First
2023-04-20 Tips for Long-Distance Cycling
2023-04-05 Cutting Cloud Costs
2023-02-08 Back to the University
2022-12-22 Rolex DateJust 36
2022-11-01 Moving to the countryside
2022-10-23 MUSE in Carré
2022-09-15 The Ultimate Freedom Bike
2022-09-11 Computer says no
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2022-04-18 Snake '97 High Scores
2022-01-14 Wearing WHOOP 4.0
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