DNS DKIM (DomainKeys Identified Mail) Record

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DNS DKIM

A DNS DKIM (DomainKeys Identified Mail) record is a type of DNS record used for email authentication. It allows the sender to associate a domain name with an email message, enabling the recipient's mail server to verify that the message was indeed sent by the authorized sender and hasn't been tampered with during transit.

What is DKIM?

DKIM is an email security standard that uses cryptographic signatures to verify the authenticity of the email sender and the integrity of the message. A DKIM signature is added to the header of an outgoing email, and the recipient’s mail server can check this signature by looking up the corresponding public key in the DNS records of the sender's domain.

How Does DKIM Work?

Email Signing (Sender's Side):

The email server signs the email with a private key associated with a domain (e.g., example.com).

The DKIM signature is added to the email header.

DNS Lookup (Receiver's Side):

The recipient's mail server queries the sender’s domain for the corresponding DKIM public key in the DNS records (specifically, the DKIM TXT record).

The recipient verifies the DKIM signature using the public key, ensuring that the email was not tampered with and that it came from the claimed domain.

DKIM DNS Record Format:

A DKIM DNS record is a TXT record that contains the public key for DKIM verification. It is structured like this:

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Host: selector._domainkey.example.com Type: TXT Value: v=DKIM1; k=rsa; p=MIIBIjANBgkqh...<public_key>

Host: This is the selector, which is a string identifying the DKIM key (e.g., selector._domainkey.example.com). The selector is used to distinguish multiple keys for the same domain.

Type: Always TXT because DKIM records are stored as text in DNS.

Value: Contains information about the DKIM version (v=DKIM1), the key type (k=rsa), and the public key (p=<public_key>).

Example DKIM Record:

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Host: default._domainkey.example.com Type: TXT Value: v=DKIM1; k=rsa; p=MIIBIjANBgkqh...<public_key>

default is the selector.

_domainkey is a standard label to indicate it's a DKIM record.

example.com is the domain.

The p= part is the public key used for verification.

When to Use DKIM:

Prevent Email Spoofing: DKIM helps protect against malicious actors impersonating your domain.

Improve Email Deliverability: Some email providers check DKIM before accepting or delivering emails. Proper DKIM records can improve your email’s chances of not being marked as spam.

Compliance: Many email services and anti-spam systems require DKIM for verification.

How to Set Up DKIM in ISPConfig:

Generate DKIM Keys:

You will need to generate a public/private key pair. This is often done via your mail server software (e.g., Postfix, Exim, or Mailgun).

You can use tools like OpenDKIM to generate the key pair.

Add the DKIM TXT Record:

Log in to ISPConfig and go to DNS Zones.

Select the domain (example.com).

Add a new TXT Record with:

Hostname: selector._domainkey (replace selector with the name of your key selector, e.g., default)

Type: TXT

Value: v=DKIM1; k=rsa; p=MIIBIjANBgkqh...<public_key> (use the public key generated earlier).

Configure Your Mail Server:

Make sure your mail server (Postfix, Exim, etc.) is configured to sign outgoing emails with the corresponding private key.

How to Verify DKIM Records:

Using dig:

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dig TXT selector._domainkey.example.com

Using Email Tools:
You can send a test email to a service like DKIMValidator or Mail-tester, which checks your DKIM records for you.

Important Notes:

Multiple DKIM Keys: You can have different selectors for different keys (e.g., default._domainkey for the current key and old._domainkey for a previous key).

Key Rotation: Periodically rotate your DKIM keys for security.