Error Domain_Not_Resolved

Error Domain_Not_Resolved

Hi,
Some days ago my Email box is returning errors to send my emails.
After I have configured DKIN and SPF. (I don't know if this the cause)
For some mail boxes I got:
contato@casamentosonthebeach.com.br  DOMAIN_NOT_RESOLVED, ERROR_CODE :DOMAIN_NOT_RESOLVED 

Note that is just a sample, I got this error for other emails.
Sometimes after I send an email, it is marked as Draft, keeping the delivered icon.
Some clients are not receiving my emails.

Can you help me ?

Best