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30 lines
1.8 KiB
Markdown
30 lines
1.8 KiB
Markdown
# Introduction
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This how to is created by the Dutch Internet Standards Platform (the organization behind [internet.nl](https://internet.nl)) and is meant to provide practical information and guidance on implementing DKIM.
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# What is DKIM?
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DKIM stands for **D**omain**K**eys **I**dentified **M**ail and is described in RFC 6376](https://tools.ietf.org/html/rfc6376) with updates in [RFC 8301](https://tools.ietf.org/html/rfc8301) and {RFC 8463](https://tools.ietf.org/html/rfc8463). It is meant to provide the owner of a domain with the means to claim that a message has actually been send by the domain's e-mail server and should therefore be considered legitimate. It works by signing every individual e-mail message with a specific key (private key), so that the receiving party can use a corresponding key (public key) published in the sending domain's DNS record to validate the e-mail authenticity and to check whether the e-mail has not been tampered with.
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# Why use DKIM?
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A common used technique used by spammers is to trick the receiving party into believing an e-mail is legitimate by using a forged sender address. This is also known as e-mail spoofing. DKIM has been designed to detect the use of spoofing. If an incoming e-mail does not have a DKIM signature or when it's DKIM signature does not validate, the receiving e-mail server should consider the e-mail to be SPAM.
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# Tips, tricks and notices for implementation
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* parked domain
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* minimum key length
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# Outbound e-mail traffic
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DNS record
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Signing in Postfix
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## Implementing DKIM in Postfix with SpamAssassin
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**Specifics for this setup**
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* Linux Debian 9.8 (Stretch)
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* SpamAssassin version 3.4.2 (running on Perl version 5.28.1)
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* Postfix 3.4.5
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* BIND 9.10.3-P4-Debian
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* OpenDKIM v2.11.0
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**Assumptions**
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* DNSSEC is used
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* Mail server is operational
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* Software packages are already installed |