Complete DKIM Setup Guide: Signing Emails Properly

DKIM Implementation Walkthrough

1. Key Generation

   # Generate private key
   openssl genrsa -out dkim.private 2048
   
   # Extract public key
   openssl rsa -in dkim.private -pubout -out dkim.public
   
2. DNS Configuration

   ; Selector: default._domainkey
   default._domainkey.example.com. IN TXT 
   "v=DKIM1; k=rsa; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQC0Jct..."
   
3. Server Integration

   # Postfix main.cf
   milter_default_action = accept
   milter_protocol = 2
   smtpd_milters = inet:localhost:8891
   non_smtpd_milters = inet:localhost:8891
   

Key Rotation Schedule

Standard

2048-bit RSA
Rotate every 90 days

High Security

4096-bit RSA
Rotate every 30 days

Experimental

ED25519
Rotate every 7 days

Troubleshooting Table

Issue	Diagnostic Command	Solution
Missing DNS Record	dig +short txt default._domainkey	Verify DNS propagation
Signature Mismatch	opendkim-testkey -d example.com	Check private key alignment
Expired Key	opendkim-testkey -v	Rotate keys immediately