Hi, @Fernando Salinas
Thank you for posting in Microsoft Q&A forum.
You may not need to specify an account for SMTP. The mail server should be configured to accept anonymous requests from and be allowed to relay from the ConfigMgr server.
Hope Gerry Hampson's reply in below thread helps:
https://social.technet.microsoft.com/Forums/en-US/c28cb701-b28e-43bc-8762-66ce97c64b3e/configuring-smtp-account-for-endpoint-protection-alerts?forum=configmanagergeneral
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