DKIM How To

Hint

• If you have issues with reverse DNS mail lookup with telnet, check network settings on VPS provider under "Networking" in SolasVM.

DKIM add new key:

• create keys and put them into /etc/opendkim/keys/domains.com/keys
• add domain to trusted.hosts
• add domain to signing.table
• add domain to key.table

systemctl restart opendkim

Generate keys two ways:

opendkim-genkey -t -s mail -d domain.com -v
opendkim-genkey -b 2048 -h rsa-sha256 -r -s mail -d domain.com -v

Add mail.txt to DNS:

cat mail.txt >> /etc/bind/zones-enabled/domain.com.zone

Test Keys:

opendkim-testkey -d domain.com -s mail -vvv
dig mail._domainkey.domain.com TXT

Need permissions:

chown -R opendkim:opendkim /etc/opendkim/
chmod go-rwx /etc/opendkim/*
chmod 700 -R /etc/opendkim/keys/

Debugging:

grep -r milter /var/log/syslog
grep -i dkim /var/log/mail.log

Notes:

• If it keys do not pass on reboot, do the following:

systemctl restart opendkim
systemctl restart postfix

• Webmail must use ports 993 and 443 or else the DKIM keys are signed twice.
• NS1 and NS2 zone files must match 100% perfect or else there are issues
• If something fails, tail log files and check systemcrt status. Also confirm permissions.

Documentation:

• Milter Guide
• Postfix Workarounds
• Postfix/DKIM Ubuntu/Debian Guide
• Key Generator

Tools:

• Online Key Validator