Why am I getting these notification errors by email and sms"sendemail:137 and sendemail:460"?

My notification isn´t work, i have this two errors in the index=_internal

-0600 ERROR sendemail:137 - Sending email. subject="prueba SEP114A", " server=""

ERROR sendemail:460 - [Errno -2] Name or service not known while sending mail to.

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