As many organizations tend to use multiple ESPs for their different email strategies (Marketing, Transactional, Billing, etc.), a DKIM selector is an important value that is used to identify the specific public key that is used to sign an email message. The selector is included as part of the DKIM signature, which is added to the headers of an email message. The selector allows the receiving server to locate the correct public key in the DNS record for the domain so that it can verify the authenticity of the message. Different selectors can be used for different purposes or parts of an organization, allowing flexibility in managing the DKIM keys.
This means that using the same DKIM selector for multiple organizations can lead to several issues and potential risks:
1. Verification Failures: DKIM verification relies on matching the selector in the email header with the public key published in DNS. If different organizations use the same selector but have different public keys, it can lead to verification failures, causing emails to be marked as unauthenticated or potentially as spam.
2. DNS Management Issues: Each organization needs to publish a DKIM record in DNS. If multiple ESPs use the same selector, they may inadvertently overwrite each other's DKIM records in DNS, leading to conflicts and errors in email authentication.
3. Troubleshooting Difficulties: When an issue arises with DKIM verification, it can be difficult to pinpoint the source of the problem if multiple organizations use the same selector. This can complicate troubleshooting efforts and delay resolution.
Make sure to use Unique DKIM Selectors for each organization to ensure independent key management and minimize the risk of conflicts.