Error: DKIM Authentication Settings Update Failed

What's Causing This Error

Several causes for this error are,

1. Recent addition or removal of a domain from the account.
2. You recently changed your DKIM key length or the DNS settings, and these changes have not propagated yet.
3. Your email service provider does not support DKIM support by default because you are using an older version.

Solution - Here's How To Resolve It

You have to check and confirm that your DNS settings are accurate and the emails with DKIM authentication are not going to the spam folder. Then you can contact your email service provider and check whether there are any issues with the authentication servers or the DKIM record and ask for their help in this situation.