Fixing DKIM Issue with G Suite using SMTP Relay

Troubleshooting DKIM Issues with Google Workspace

It can be annoying to experience a DKIM failure with your Gsuite email solution, particularly if you are scanning outbound emails through a secure email gateway. Receivers interpret the "dkim=neutral (body hash did not verify)" result—which frequently occurs during the setup of a custom DKIM key in Gsuite—as a failure.

It's important to comprehend how DKIM functions in a setup where Gmail sends emails to a secure email gateway (SEG) and then relays them via the Gmail SMTP relay. The purpose of this post is to assist you in properly diagnosing and fixing these DKIM issues.

Recognizing the Functions of DKIM Scripts

By extracting the DKIM header from the email and requesting the DKIM key linked to the domain and selector from DNS, the given Python script assists in the verification of DKIM signatures. The validity of the DKIM signature is checked by this script using the dkim.verify function, which is essential for preserving the integrity and authenticity of emails. While message_from_bytes transforms the email from a bytes-like object to a readable message format, dns.resolver.resolve requests DNS for the TXT record associated with the DKIM key.

DKIM signing is configured on a secure email gateway (SEG) using the Postfix configuration script. The script makes sure that outgoing emails are correctly signed with the DKIM key by installing and configuring OpenDKIM with the necessary parameters, such as Canonicalization for the DKIM signature and SyslogSuccess for logging operations. The DKIM DNS record checking and updating process is automated by the bash script, which facilitates the management of DKIM keys and guarantees their proper configuration for your domain.

import dkim
import dns.resolver
from email import message_from_bytes
def check_dkim(email_bytes):
    msg = message_from_bytes(email_bytes)
    dkim_header = msg['DKIM-Signature']
    domain = dkim_header.split('@')[1].split(' ')[0]
    selector = dkim_header.split('=')[1].split(';')[0]
    dns_response = dns.resolver.resolve(f'{selector}._domainkey.{domain}', 'TXT')
    dkim_key = dns_response[0].to_text().strip(' "')
    dkim.verify(email_bytes, dkim_key)
email_path = 'path/to/email.eml'
with open(email_path, 'rb') as f:
    email_bytes = f.read()
check_dkim(email_bytes)

sudo apt-get install opendkim opendkim-tools
sudo nano /etc/opendkim.conf
AutoRestart             Yes
AutoRestartRate         10/1h
Syslog                 yes
SyslogSuccess          Yes
LogWhy                 Yes
Canonicalization       relaxed/simple
Mode                   sv
SubDomains             no

#!/bin/bash
DOMAIN="yourdomain.com"
SELECTOR="default"
DKIM_RECORD=$(dig TXT ${SELECTOR}._domainkey.${DOMAIN} +short)
if [[ -z "$DKIM_RECORD" ]]; then
  echo "DKIM record not found for $DOMAIN with selector $SELECTOR"
else
  echo "DKIM record for $DOMAIN: $DKIM_RECORD"
fi
sudo opendkim-genkey -s ${SELECTOR} -d ${DOMAIN}
sudo mv ${SELECTOR}.private /etc/opendkim/keys/${DOMAIN}/
sudo chown opendkim:opendkim /etc/opendkim/keys/${DOMAIN}/${SELECTOR}.private

Handling Email Gateway DKIM Issues

One typical problem when utilizing Google Workspace with a secure email gateway is that the gateway may change the body text of the email, which can lead to the DKIM signature failing verification. Make sure the gateway is set up to maintain the integrity of the email body in order to lessen this. An alternative strategy would be to set up the gateway to re-sign the email using the company's DKIM key prior to it being sent to the Gmail SMTP relay.

It's also important to know the sequence of events and the location of the DKIM signing. A mismatch may occur if the SEG makes changes to the email after Google has signed it. Failures can be avoided by configuring SEG to handle DKIM keys correctly. Email integrity must be preserved by making sure Google Workspace, SEG, and the SMTP relay are all in sync.

Concluding Remarks on DKIM Configuration Difficulties

When utilizing an SMTP relay and SEG, fixing DKIM errors in Google Workspace requires a grasp of how each part works with the other. Making ensuring the SEG doesn't change the email content in a way that renders the DKIM signature invalid is crucial. Maintaining the integrity and validity of outgoing messages requires setting up both the SEG and Google Workspace to handle DKIM keys correctly.

You can troubleshoot and resolve DKIM issues effectively by using the offered scripts and parameters. You can help keep your email system safe and dependable by routinely checking your DKIM setup with DNS tools and email validators. Maintaining accurate synchronization among all elements will avert DKIM malfunctions and improve the security of your emails.