User doesn't receive workflow notifications

I´m trying to figure out why one user can't receive email notifications from smartsheet.

Context: I have a smarthseet to track QA Auduts and this specific workflow is to send the audited agents an update requesting to sign off their results. Due the nature of data in the sheet, Agents don't have access, so once the QA specialist tracks the results, the request to update agents sign off is triggered when the QA Specialist changes the Audit status to "complete". This is a list of more than 300 agents that have received their email notification with the exception of one person. I personally have checked agent's email, junk folder and have added smartsheet domains to the "safe senders" in outlook but still not working. Any ideas please?