Using classic Outlook for Windows in business environments
If you must create DKIM records, add 2 new CNAME records with the following entry:
Record type: CNAME
Name: selector1._domainkey
Value: selector1-goldenstring-com._domainkey.goldenstring.onmicrosoft.com
Record type: CNAME
Name: selector2._domainkey
Value: selector2-goldenstring-com._domainkey.goldenstring.onmicrosoft.com
and go to this address to enable DKIM signing https://security.microsoft.com/authentication?viewid=DKIM (I have onmicrosoft.com as my default signing domain)