DKIM Selector settings
You can turn off this DKIM selector signing using this switch.
DomainKeys Identified Mail (DKIM) defines a mechanism by which email messages can be cryptographically signed,
and they are signed using a specific 'selector' which is essentially a named public/private key pair.
The recipient server looks up the public key using a DNS check. The signing server takes a hash of the email, and encrypts it using the
private key. The recipient server can then decrypt the hash and check it against a hash it makes of the email to verify the email has
not been tampered with. Be sure to republish your selector DNS entries if you change any settings and be aware that if some email has already been signed but not yet
delivered changing the selector settings may result in the email with signatures already generated email becoming invalidated and not accepted by remote servers.
If you wish to change settings it is best to create a new selector, DNS record and start using that to sign email, and disable old selectors that are no longer required.